Grout for 12 inch tiles that are 3/8 inch thick, set with 1/8 inch joints, runs about 7.2 pounds per 100 square feet, so a 25 pound bag of sanded grout covers roughly 348 square feet. Widen the joints to 1/4 inch and the same floor takes 14.1 pounds per 100 square feet. Drop to a 2 inch mosaic at 1/8 inch and it takes 26.0.
Three inputs set the number: the width of the joint, the thickness of the tile, and the size of the tile face. Joint width and thickness scale the grout almost one for one, so doubling either one doubles the pounds. Tile size works the other way, because small tiles carry more joint line in every square foot of floor. A 24 inch tile needs half the grout of a 12 inch tile at the same joint and thickness, and a 1 inch mosaic at that joint needs about 6.4 times as much, even though the mosaic is the thinner tile.
Manufacturers publish the answer as a coverage chart: square feet per bag for a grid of tile sizes and joint widths. Two such charts, from CUSTOM Building Products and from TEC Specialty Products, sit behind the figures on this page. Converted to pounds per 100 square feet, they stay between 0.91 and 1.06 of each other on the shared cells for tiles 6 inches and larger, and a single joint-volume formula reproduces both to within about 7%. The larger uncertainties are on the floor: joint depth, the true width of the joints, the shape of the tile edge, and the last half bag.
The joint is a thin box with a known volume
Grout fills the gap between tiles, and that gap is a box as long as the joint line, as wide as the joint and as deep as the tile is thick. Everything else is bookkeeping.
Take a tile of length L and width W, both in inches, laid with a joint of width j. Tiles sit on a grid whose spacing is the tile plus one joint, so each grid cell measures L + j by W + j. A cell holds one tile face plus an L-shaped strip of joint along two of its sides. With a tile thickness t, the volume of joint in one cell is t times the joint area:
Divide by the area of the cell and multiply by 144 square inches per square foot, and the result is the cubic inches of joint under each square foot of tiled floor:
Here is the formula at work for a 12 inch tile, 3/8 inch thick, with 3/16 inch (0.1875 inch) joints:
- The grid cell is 12.1875 by 12.1875 inches, an area of 148.54 square inches.
- The tile face is 144 square inches, so the joint area in the cell is 4.54 square inches.
- Times the thickness of 0.375 inch, that is 1.70 cubic inches of joint per tile.
- One square foot holds 144 / 148.54 = 0.9695 cells.
- The joint volume is 1.70 x 0.9695 = 1.65 cubic inches per square foot of floor.
A shorter version drops the j-squared term and treats each tile as if it filled its whole cell: V is about 144 t j (1/L + 1/W). For a 12 inch tile at 1/8 inch it gives 1.1250 cubic inches per square foot, against 1.1077 for the grid version, 1.6% more. The two agree closely on large tiles and narrow joints, and part ways on small tiles and wide ones. The grid version is 0.99 of the short version for a 24 inch tile at 1/8 inch, 0.94 for a 12 inch tile at 1/2 inch, and 0.84 for a 1 inch tile at 1/8 inch. Both versions turn up in the manufacturers' numbers below.
Turning cubic inches into pounds of dry grout
A bag is sold by weight, so the volume needs a conversion constant: pounds of dry grout per cubic inch of finished joint. This guide writes it as rho. It is not a material density in the textbook sense. It folds together the density of the cured joint, how well the joint is packed, the water that leaves, and any allowance a manufacturer builds into a chart. That is why it cannot be looked up and is backed out of published coverage instead.
CUSTOM Building Products publishes a coverage chart for its sanded polymer-modified cement grout, Polyblend Plus. For a 25 lb bag it lists 348 square feet at 12 x 12 x 3/8 inch tile with 1/8 inch joints. That is 25 / 348 = 0.0718 pounds per square foot, or 7.18 pounds per 100 square feet. Dividing by the joint volumes above gives:
- With the short formula (1.1250 cubic inches per square foot): rho = 0.0639 pounds per cubic inch.
- With the grid formula (1.1077 cubic inches per square foot): rho = 0.0649 pounds per cubic inch.
Both land at about 0.064, so a figure of roughly 0.064 pounds of dry grout per cubic inch of finished joint (110.6 pounds per cubic foot of joint) is a fair summary of that one cell. One cell is a thin test, though. The real question is whether a single constant holds across the whole chart.
CUSTOM's chart as pounds per 100 square feet
The chart covers 16 tile sizes at five joint widths, 80 cells in all, each one a number of square feet per 25 lb bag. Pounds per 100 square feet is 2,500 divided by the coverage, so 348 square feet becomes 7.2 and 24 square feet becomes 104.2. The table below makes that conversion for every cell. Multiply the table value by your area and divide by 100 to get pounds.
| Tile size (inches, length x width x thickness) | 1/8" | 3/16" | 1/4" | 3/8" | 1/2" |
|---|---|---|---|---|---|
| 1 x 1 x 1/4 | 46.3 | 62.5 | 75.8 | 92.6 | 104.2 |
| 2 x 2 x 1/4 | 26.0 | 36.8 | 46.3 | 62.5 | 75.8 |
| 3 x 3 x 1/4 | 18.1 | 26.0 | 33.8 | 46.3 | 58.1 |
| 4.25 x 4.25 x 1/4 | 13.0 | 19.1 | 24.8 | 35.2 | 44.6 |
| 6 x 6 x 1/4 | 9.4 | 13.8 | 18.0 | 26.0 | 33.3 |
| 8 x 8 x 3/8 | 10.7 | 15.8 | 20.7 | 30.1 | 39.1 |
| 12 x 12 x 3/8 | 7.2 | 10.7 | 14.1 | 20.7 | 27.2 |
| 16 x 16 x 3/8 | 5.4 | 8.1 | 10.7 | 15.8 | 20.7 |
| 18 x 18 x 3/8 | 4.8 | 7.2 | 9.5 | 14.1 | 18.5 |
| 20 x 20 x 3/8 | 4.4 | 6.5 | 8.6 | 12.8 | 16.8 |
| 24 x 24 x 3/8 | 3.6 | 5.4 | 7.2 | 10.7 | 14.1 |
| 6 x 24 x 3/8 | 9.0 | 13.2 | 17.5 | 25.5 | 33.3 |
| 12 x 24 x 3/8 | 5.4 | 8.1 | 10.7 | 15.8 | 20.7 |
| 6 x 36 x 3/8 | 8.4 | 12.4 | 16.3 | 24.0 | 31.3 |
| 9 x 36 x 3/8 | 6.0 | 9.0 | 11.8 | 17.5 | 22.9 |
| 12 x 48 x 3/8 | 4.5 | 6.8 | 9.0 | 13.2 | 17.5 |
Pounds of dry sanded grout per 100 square feet, from CUSTOM's 25 lb coverage chart (2,500 divided by square feet per bag). Joint widths are the nominal 1/8, 3/16, 1/4, 3/8 and 1/2 inch of the chart's column headings.
A project that falls between rows can lean on three regularities in the table.
- Joint width is close to proportional. A 12 inch tile needs 7.2 pounds at 1/8 inch and 14.1 at 1/4 inch, a ratio of 1.97, and 27.2 at 1/2 inch. The chart's coverage numbers for those widths are 348, 177 and 92 square feet.
- Tile size is close to inversely proportional. A 24 inch tile needs 3.6 pounds at 1/8 inch against 7.2 for a 12 inch tile, a ratio of 1.98. The spread across the whole table is 28.7 to one, from 3.6 pounds (24 x 24 at 1/8 inch) to 104.2 (1 x 1 at 1/2 inch).
- Thickness hides in the row labels. The 6 x 6 row needs 9.4 pounds at 1/8 inch, less than the 10.7 of the 8 x 8 row, even though the 6 inch tile is the smaller one. The 6 inch tile is listed at 1/4 inch thick and the 8 inch tile at 3/8 inch, and a thicker tile makes a deeper joint.
The chart is a 25 lb chart. CUSTOM also lists a 7 lb box, and that chart is the same one scaled down: across all 80 cells, 7/25 of the 25 lb coverage matches the 7 lb figure to within 0.56 square feet (0.25 on average). A 7 lb box therefore covers 66 square feet of 12 inch tile at 3/16 inch, against 234 for the 25 lb bag.
For metric work, one pound per 100 square feet is 0.0488 kilograms per square metre. The 12 inch tile at 3/16 inch needs 10.7 pounds per 100 square feet, which is 0.52 kilograms per square metre, and a 25 lb (11.34 kg) bag covers 21.7 square metres of it. The weight converter handles other pound and kilogram conversions.
How closely one formula reproduces the chart
The test: take the grid formula, set rho to 0.064, compute pounds per 100 square feet for each of the 80 cells, and compare with the chart. The difference below is formula minus chart, as a percentage of the chart.
| Tile size | 1/8" | 3/16" | 1/4" | 3/8" | 1/2" |
|---|---|---|---|---|---|
| 1 x 1 x 1/4 | +4.4% | +7.2% | +9.5% | +17.2% | +22.9% |
| 2 x 2 x 1/4 | +1.0% | +2.8% | +4.4% | +7.2% | +9.5% |
| 3 x 3 x 1/4 | -0.3% | +1.0% | +0.9% | +4.4% | +5.1% |
| 6 x 6 x 1/4 | -1.0% | -0.4% | +0.4% | +1.0% | +2.2% |
| 12 x 12 x 3/8 | -1.3% | -1.2% | -1.1% | -0.2% | -0.3% |
| 24 x 24 x 3/8 | -1.7% | -1.6% | -1.3% | -1.2% | -1.1% |
| 6 x 24 x 3/8 | -1.7% | -1.2% | -1.4% | -0.7% | -0.7% |
| 12 x 48 x 3/8 | -1.7% | -1.7% | -1.7% | -1.2% | -1.4% |
Formula (grid version, rho = 0.064 lb per cubic inch) against CUSTOM's chart, selected rows of the 80 cells.
For the 60 cells whose shorter side is 6 inches or more, the formula lands within 1.7% below to 2.2% above the chart, 1.0% below on average. The best single constant for those 60 cells is 0.0647 pounds per cubic inch, ranging from 0.0626 to 0.0651 cell by cell. Rounding it to 0.064 makes the formula ask for about 1% less grout than the chart on average, a difference smaller than the slack in any bag.
Across all 80 cells, 73 fall within 5% and 70 within 3%. The seven cells that miss by more than 5% are all in the 1, 2 and 3 inch rows, and in every one the formula asks for more grout than the chart lists. The extreme is the 1 inch tile at 1/2 inch joints, where the formula gives 128.0 pounds per 100 square feet and the chart gives 104.2.
A second manufacturer's chart
A constant fitted to one chart says little about grout in general. TEC Specialty Products publishes a second chart, on its sheet for AccuColor Premium Sanded Grout (product 650, updated September 2026), and it makes a useful test. TEC lists coverage in square feet per pound rather than per bag. Its chart has 14 tile sizes at 1/8, 1/4, 3/8 and 1/2 inch joints, 50 populated cells (the 1 x 1 and 2 x 2 rows give only the 1/8 inch figure). Converted to pounds per 100 square feet (100 divided by square feet per pound):
| Tile size | 1/8" | 1/4" | 3/8" | 1/2" |
|---|---|---|---|---|
| 1 x 1 x 1/4 | 54.9 | n/a | n/a | n/a |
| 2 x 2 x 1/4 | 27.5 | n/a | n/a | n/a |
| 3 x 6 x 1/4 | 13.7 | 27.5 | 41.2 | 54.9 |
| 4.25 x 4.25 x 1/4 | 12.9 | 25.8 | 38.8 | 51.5 |
| 6 x 6 x 1/4 | 9.1 | 18.3 | 27.5 | 36.6 |
| 6 x 24 x 3/8 | 8.6 | 17.2 | 25.7 | 34.4 |
| 6 x 36 x 3/8 | 8.0 | 16.0 | 24.0 | 32.1 |
| 8 x 8 x 3/8 | 10.3 | 20.6 | 30.9 | 41.2 |
| 10 x 10 x 3/8 | 8.2 | 16.5 | 24.7 | 32.9 |
| 12 x 12 x 3/8 | 6.9 | 13.7 | 20.6 | 27.5 |
| 12 x 24 x 3/8 | 5.1 | 10.3 | 15.4 | 20.6 |
| 18 x 18 x 3/8 | 4.6 | 9.1 | 13.7 | 18.3 |
| 20 x 20 x 3/8 | 4.1 | 8.2 | 12.3 | 16.5 |
| 24 x 24 x 3/8 | 3.4 | 6.9 | 10.3 | 13.7 |
Pounds of dry grout per 100 square feet, from TEC's coverage per pound for AccuColor Premium Sanded Grout (650). "n/a" means the sheet gives no figure for that cell.
Each TEC row scales exactly with joint width. The 3 x 6 tile, for example, is listed at 7.29, 3.64, 2.43 and 1.82 square feet per pound at 1/8, 1/4, 3/8 and 1/2 inch: each figure is the 1/8 inch figure times 1/8 over the joint width, to the rounding of the sheet.
Fitting TEC's cells to the joint-volume formulas gives a different picture from CUSTOM's. Every one of the 50 TEC cells falls within 0.3% of the short, flat formula with a constant of 0.0610 pounds per cubic inch (0.0609 at the low end, 0.0611 at the high end, 105.4 pounds per cubic foot of joint). The grid version does not fit TEC as tightly: its constant would have to range from 0.0615 to 0.0731. CUSTOM's chart behaves the other way around. Its cells at 6 inches and up follow the grid version at about 0.0647, and its mosaic rows fall below the grid version's predictions. The two sets of numbers are consistent with the formulas, and the data say nothing about how either maker produced its chart.
The two constants sit 6% apart (0.0610 against 0.0647), which is small next to the other uncertainties in a tile job. Placed side by side, cell by cell:
| Tile, joint | CUSTOM lb/100 sq ft | TEC lb/100 sq ft | CUSTOM / TEC |
|---|---|---|---|
| 1 x 1, 1/8" | 46.3 | 54.9 | 0.84 |
| 4.25 x 4.25, 1/2" | 44.6 | 51.5 | 0.87 |
| 6 x 6, 1/4" | 18.0 | 18.3 | 0.98 |
| 12 x 12, 1/8" | 7.2 | 6.9 | 1.05 |
| 12 x 12, 1/4" | 14.1 | 13.7 | 1.03 |
| 12 x 12, 1/2" | 27.2 | 27.5 | 0.99 |
| 24 x 24, 1/8" | 3.6 | 3.4 | 1.06 |
| 24 x 24, 1/2" | 14.1 | 13.7 | 1.03 |
Across the 42 cells that both charts list, the ratio of CUSTOM's pounds to TEC's runs from 0.84 to 1.06. Restricted to the 36 shared cells for tiles 6 inches and larger, it runs from 0.91 to 1.06 and averages 1.02. Narrow joints on large tiles are where CUSTOM asks for up to 6% more, and small tiles are where it asks for up to 16% less (the 1 x 1 mosaic at 1/8 inch is 0.84, the 4.25 x 4.25 tile at 1/2 inch 0.87). This is a comparison of two data points, not a ranking: a higher pound count means that sheet's assumptions use more grout per square foot, not that either product is better or worse.
Against the formula at 0.064, TEC's 40 cells for tiles 6 inches and larger run from 7.0% below to 4.1% above. Over all 50 TEC cells, the range is 12.4% below (the 3 x 6 tile at 1/2 inch) to 4.1% above. So the 0.064 constant is a reasonable planning value for both charts, with errors that stay within a few percent on large tiles and grow on small tiles at wide joints.
Both makers say what the charts are. CUSTOM's note reads: "Chart for estimating purposes. Coverage may vary based on installation practices and jobsite conditions." It then points to the maker's own materials calculator for other tile and joint sizes. TEC's sheet says: "Figures shown in the chart are presented only as guidelines." Neither the CUSTOM chart page and data sheet nor the TEC sheet uses the word waste. Because every cell is proportional to joint volume, any allowance either maker has folded in is a percentage of the figure, not a fixed overage, and it cannot be separated from rho.
Joint depth, the assumption inside every cell
The formula takes the joint depth as the full tile thickness, and both charts list a thickness beside every tile size, which is how a thickness enters the numbers. A real grout line may not be filled to full depth, and the charts have no input for that.
Two manufacturer sentences bear on it. TEC's sheet says the joints between the tiles "should be free from foreign materials, and be at least 2/3 of the thickness of the tile in depth." CUSTOM's data sheet says to "Remove spacers and ensure that the grout joints are uniform in depth and width and free of loose debris, contaminants and excess mortar." The first sets a floor of two thirds of the tile thickness for the clear space; the second makes the point that depth is a thing to check, not assume.
How much grout that depth is worth can be read off the formula, since pounds are directly proportional to depth. For a 12 inch tile, 3/8 inch thick, with 3/16 inch joints (the chart lists 10.7 pounds per 100 square feet, the formula 10.6):
| Joint filled to | Depth (inches) | lb per 100 sq ft |
|---|---|---|
| Full tile thickness | 0.375 | 10.6 |
| 3/4 of thickness | 0.281 | 7.9 |
| 2/3 of thickness | 0.250 | 7.0 |
| 1/2 of thickness | 0.188 | 5.3 |
A joint that is only two thirds full takes about a third less grout than the chart implies. Mortar that squeezes up into the joint is one way the filled depth falls short of the tile thickness, and the TEC sentence above is aimed at exactly that. Neither chart can see it, so the printed numbers are best read as the figure for a clean, full-depth joint.
The other side of the same proportionality is thickness. If a tile is thicker than its chart row, the grout rises with it. For the same 12 inch tile at 3/16 inch joints:
| Tile thickness (inches) | lb per 100 sq ft |
|---|---|
| 1/4 | 7.0 |
| 3/8 | 10.6 |
| 1/2 | 14.1 |
| 5/8 | 17.6 |
| 3/4 | 21.1 |
The easy way to go wrong is a thick tile in a thin row. CUSTOM lists the 6 x 6 tile at 1/4 inch. If the tile you are buying is 3/8 inch thick, 3/16 inch joints take 20.6 pounds per 100 square feet, not the 13.8 the chart gives for that row, 1.5 times as much. Measure the tile with a tape or caliper before picking a row, and use the tile's own thickness in the formula.
Measured joint width and edge shape
Joint width is the largest lever in the formula and the one most often taken from a label instead of a measurement. The figure that matters is the width of the joint after the tile is set, not the width of the spacer.
| Joint width | 12 x 12 x 3/8: lb per 100 sq ft | 24 x 24 x 3/8: lb per 100 sq ft |
|---|---|---|
| 1/16" | 3.6 | 1.8 |
| 1/8" | 7.1 | 3.6 |
| 3/16" | 10.6 | 5.3 |
| 1/4" | 14.0 | 7.1 |
| 5/16" | 17.3 | n/a |
| 3/8" | 20.6 | n/a |
Formula, grid version, rho = 0.064.
A joint that measures 3/16 inch where the plan said 1/8 inch raises the 12 inch tile from 7.1 to 10.6 pounds, an increase of 50%. A joint measured at 5/32 inch instead of 1/8 inch is 25% wider and needs 25% more grout. These errors dwarf the 6% gap between the two charts. The sanded CUSTOM grout is rated for joints from 1/8 to 1/2 inch, and the non-sanded one for joints up to 1/8 inch (more on the difference below), so the 1/16 inch row in the table is shown only to give the scale.
Edge shape is the other geometry the charts cannot see. A tile with a chamfered, rounded or pressed edge leaves more room at the top of the joint than a square-edged one. The simplest shape to quantify is a straight bevel of size c on each of the two tile edges that face a joint. Each bevel removes a right triangle of area c squared over two from the tile's section, so the joint's cross-section grows by c squared, on top of the j times t of a square-edged joint. The extra grout, as a percentage, is c squared divided by j times t. For a tile 3/8 inch thick the bevel sizes below are illustration inputs, not measured product data:
| Bevel on each edge | Extra grout at 1/8" joints | Extra grout at 1/4" joints |
|---|---|---|
| 1/32" | 2.1% | 1.0% |
| 1/16" | 8.3% | 4.2% |
| 1/8" | 33.3% | 16.7% |
For the 12 inch tile at 1/8 inch joints, a 1/16 inch bevel on each side lifts the figure from 7.1 to 7.7 pounds per 100 square feet, and a 1/8 inch bevel to 9.5. A barely eased edge costs little, and a pronounced bevel costs a third more. A narrow joint magnifies the effect, because the bevel is fixed in size while the joint it sits beside is small. Both charts list tile size and thickness only. They have no input for edge shape, so a tile with a visible edge treatment sits on the high side of its row.
Mosaics and the small-tile rows
The small-tile rows are the only part of CUSTOM's chart where the formula and the chart part ways by more than a few percent, and the gap grows with joint width. The same rows in the two charts also disagree with each other: the 1 x 1 tile at 1/8 inch is 46.3 pounds per 100 square feet in CUSTOM's chart and 54.9 in TEC's.
| Tile, joint | CUSTOM chart | TEC chart | Formula (0.064) |
|---|---|---|---|
| 1 x 1, 1/8" | 46.3 | 54.9 | 48.4 |
| 1 x 1, 1/4" | 75.8 | n/a | 82.9 |
| 1 x 1, 1/2" | 104.2 | n/a | 128.0 |
| 2 x 2, 1/8" | 26.0 | 27.5 | 26.3 |
| 2 x 2, 1/2" | 75.8 | n/a | 82.9 |
| 3 x 3, 1/8" | 18.1 | n/a | 18.1 |
| 3 x 3, 1/2" | 58.1 | n/a | 61.1 |
Pounds of dry grout per 100 square feet, 1/4 inch tile thickness. The 3 x 6 row, which TEC lists, is not in CUSTOM's chart.
The table shows a gap and stops there: neither sheet states why its small-tile rows run the way they do. For an order, the practical reading is a range. A 1 x 1 mosaic at 1/8 inch runs from 46.3 (CUSTOM) through 48.4 (formula) to 54.9 (TEC), and a 2 x 2 at 1/8 inch from 26.0 through 26.3 to 27.5. At wider joints the formula is the high estimate and CUSTOM's chart the low one.
One input changes the answer more than the choice of chart. The formula treats the stated tile size as the tile face and adds the joint on top. If a sheet's stated 1 x 1 inch is instead the repeat distance from one tile to the next, with a 1/8 inch joint inside it, the tile face is 7/8 inch, and the grid formula gives 54.0 pounds per 100 square feet in place of the 48.4 for a 1 inch face: 12% more. The repeat distance can be measured on the sheet in a minute, and that measurement is worth more than the decision about which chart to trust.
Sanded and non-sanded grout
CUSTOM's product page says its sanded grout "accommodates 1/8″-1/2″ (3.1-12.7 mm) joints" and its non-sanded grout "accommodates joints up to 1/8″ (3 mm)." Its data sheet for the sanded product also cautions that some ceramic, glass, metal, marble or stone tiles can be scratched or damaged by the silica aggregate filler, and recommends testing a small area first. The choice between the two is a joint width and tile surface decision before it is a quantity decision.
The quantities differ a little. CUSTOM's non-sanded chart (per 10 lb of grout, at joint widths of 1/16 and 1/8 inch) asks for slightly less per square foot than the sanded chart at 1/8 inch: across the 15 tile sizes the two charts share, non-sanded runs from 0.94 to 0.96 of the sanded pounds, 0.95 on average. For 12 inch tile at 1/8 inch that is 6.8 pounds per 100 square feet, against 7.2 for sanded. Using the sanded table for a non-sanded job would over-order by about 5%, which is within the usual margin; using it for a different grout type altogether (epoxy, urethane, premixed) has no basis in either chart. Check the coverage table that comes with the grout you actually buy.
From pounds to bags, and what the last half bag costs
Bags come in fixed sizes, so the final step is rounding. For 12 inch tile at 3/16 inch joints (10.7 pounds per 100 square feet), here is what different areas need. The "+10%" columns add a 10% margin, which is an illustration input chosen for the table: no manufacturer source gives a waste figure.
| Area (sq ft) | lb needed | 25 lb bags | 7 lb boxes | lb with +10% | 25 lb bags with +10% |
|---|---|---|---|---|---|
| 25 | 2.7 | 1 | 1 | 2.9 | 1 |
| 50 | 5.3 | 1 | 1 | 5.9 | 1 |
| 100 | 10.7 | 1 | 2 | 11.8 | 1 |
| 150 | 16.0 | 1 | 3 | 17.6 | 1 |
| 200 | 21.4 | 1 | 4 | 23.5 | 1 |
| 300 | 32.1 | 2 | 5 | 35.3 | 2 |
| 500 | 53.4 | 3 | 8 | 58.8 | 3 |
Bag sizes turn those pounds into purchases in three steps.
First, small areas are really a box-versus-bag decision. A 45 square foot bathroom floor of this tile takes 4.8 pounds, which one 7 lb box covers (the box chart says 66 square feet). A 100 square foot floor takes 10.7 pounds, which is two boxes (14 pounds) or one 25 lb bag with 14.3 pounds to spare. Which is cheaper depends on local prices, which this page does not track.
Second, the margin matters only where the need is near a bag boundary. At 300 square feet the need is 32.1 pounds, two bags either way, and with 10% added it is 35.3, still two. At 500 square feet it is 53.4 pounds and three bags with or without the margin. A margin earns its keep only when a job sits within a few pounds of a boundary, and a joint that is a sixteenth of an inch wider than planned moves the need by far more than 10%.
Third, whatever allowance a chart carries is already inside its number. Both makers describe their figures as estimates or guidelines, in the sentences quoted earlier. A figure near a bag boundary is a reason to measure the joints again, not a reason to stack a second margin on top of the first.
Mixed grout cannot be kept for the leftovers. TEC's sheet puts the working time (pot life) of its sanded grout, mixed with water and slaked, at "approximately 1 to 2 hours", so each batch should cover only as much floor as can be finished in that time. Unmixed grout is a different matter: the same sheet says to store it in a cool, dry location, not to store open containers, and gives a maximum shelf life of 18 months from the date of manufacture in a properly stored, unopened package. A spare, unopened bag is a usable leftover; a spare bucket of mixed grout is not.
Six jobs, start to finish
The table works six jobs through the chart row, the formula and the bag count. "Formula" uses the grid version with rho = 0.064. The bag counts use 25 lb bags except where 7 lb boxes are noted.
| Job | Chart row | Chart lb/100 sq ft | Need (chart) | Need (formula) | Bags / boxes |
|---|---|---|---|---|---|
| 45 sq ft bath floor | 12 x 12, 3/16" | 10.7 | 4.8 lb | 4.7 lb | one 7 lb box |
| 200 sq ft kitchen | 12 x 24, 3/16" | 8.1 | 16.1 lb | 15.9 lb | one bag, or three 7 lb boxes |
| 1,200 sq ft great room | 24 x 24, 1/8" | 3.6 | 43.6 lb | 42.9 lb | two bags |
| 30 sq ft backsplash | 2 x 2, 1/8" | 26.0 | 7.8 lb | 7.9 lb | two 7 lb boxes, or one bag |
| 60 sq ft shower | 3 x 3, 1/4" | 33.8 | 20.3 lb | 20.4 lb | one bag, or three 7 lb boxes (four with 10% added) |
| 300 sq ft floor | 12 x 12, 1/4" | 14.1 | 42.4 lb | 41.9 lb | two bags |
Need (chart) is the area divided by the chart's square feet per bag, times the bag weight, from CUSTOM's chart; it can differ by a few tenths of a pound from area / 100 times the rounded table value. Need (formula) is the grid formula at 0.064.
The kitchen is the cleanest case. A 12 x 24 tile at 3/16 inch needs 16.1 pounds for 200 square feet. One 25 lb bag covers it with 8.9 pounds left over, and the chart says that bag would cover 310 square feet of this tile. Three 7 lb boxes would be 21 pounds, covering the job with 4.9 pounds spare; the bag is the larger overbuy but is one purchase.
The great room shows how little the chart and the formula disagree on large tiles, 43.6 pounds against 42.9, and how decisively the joint width matters. At 1/8 inch, two bags (50 pounds) cover the 43.6 with 6.4 pounds spare, about 15% over the need, and adding 10% for margin (48.0 pounds) still fits in two bags. If the installer ends up with 3/16 inch joints, the chart's 461 square feet per bag puts the need at 65.1 pounds, which is three bags. The tile, the room and the grout did not change; a sixteenth of an inch of joint did.
The 300 square foot floor is the same tile at several joint widths. Using the chart's 12 inch row, the need is 21.6 pounds at 1/8 inch, 32.1 at 3/16, 42.4 at 1/4 and 62.0 at 3/8 inch, which is one, two, two and three 25 lb bags. Across that range the order runs from one bag to three, which is the reason to measure the joints on a real sample before ordering.
The shower is the one case where a margin changes the box count. The need is 20.3 pounds (20.4 by formula), so three 7 lb boxes (21 pounds) are just enough with no margin. With 10% added the need is 22.3 pounds and the order rises to four boxes. A 25 lb bag covers the 10% version with 2.7 pounds to spare.
Pairing the grout estimate with the tile count
The tile calculator is the other half of this estimate, though it is worth being exact about what it does. It takes the area, tile width, tile length and a waste percentage (15% by default), and returns the number of tiles and the area including waste. It treats the joint as a fixed 1/8 inch, counting each tile as tile plus 1/8 inch in both directions, which is the same tile-plus-joint grid the formula above uses. It does not return grout.
Two things carry over. First, use the room area, not the tile-order area, for grout. Extra tile bought as a cutting allowance does not add joint, and the 15% added by the tile calculator should not be fed into the grout table. Second, if your joints are wider than 1/8 inch, the tile calculator's count runs slightly high, because it spaces tiles for a 1/8 inch joint and wider joints let each tile cover more floor; the grout table above takes the actual joint. For an irregular room, the square footage calculator splits it into rectangles, and the flooring calculator covers the flooring side of the same room.
The same conversion of a printed yield into a quantity for your own room applies to the neighbouring jobs: how much paint you need works it for coverage per gallon, and how many bags of concrete works it for bag yields. The homeowners hub collects the home-project guides in one place.
Reading a bag against your own floor
The process takes ten minutes with a tape measure and a pencil.
- Measure one tile's length, width and thickness, and write them down.
- Dry-lay a few tiles with your spacers and measure the actual gap between them, in sixteenths of an inch, in at least three places.
- Find the row that matches your tile in the table above, or compute it with the formula, using your measured thickness.
- Take the column for your measured joint width. If it falls between columns, interpolate by joint width; the numbers are close to proportional.
- Multiply the table value by your area in square feet, divided by 100.
- Compare with the coverage chart on the bag you are buying, since that chart takes precedence for that product, and round up to a whole bag or box.
The two charts above land between 0.91 and 1.06 of each other on tiles 6 inches and larger. A joint that measures 5/32 inch instead of 1/8 inch moves the answer by 25%, so the tape measure matters more than the choice of chart.
Sources
- CUSTOM Building Products, Polyblend Plus Sanded Grout product page: coverage charts for the 25 lb bag and the 7 lb box (16 tile sizes at five joint widths) and the product description with its joint range. Checked November 3, 2026.
- CUSTOM Building Products, Polyblend Plus Non-Sanded Grout product page: coverage chart for the 10 lb pack at 1/16 and 1/8 inch joints and the product description. Checked November 3, 2026.
- CUSTOM Building Products, Polyblend Plus Sanded Grout technical data sheet TDS-360 (printed publication date 3/22/2023): the same coverage chart, the estimating note, the silica-aggregate caution and the joint-preparation sentence. Checked November 3, 2026.
- TEC Specialty Products, AccuColor Premium Sanded Grout (650) product data sheet, updated September 2026: coverage per pound for 14 tile sizes, joint-depth sentence, pot life, storage and shelf life. Checked November 3, 2026.
- Joint volumes, the fitted constants, every pounds-per-100-square-feet figure, the deviation tables and the worked jobs: derived from the four documents above using the formulas on this page. Epoxy, urethane and premixed grouts, and charts from other manufacturers, are not in the tables.