Per 100 square feet, a 4 in compacted patio base is 1.23 cubic yards, about 2.3 tons of crushed stone at WSDOT's compacted weight of 1.85 tons per cubic yard. A 6 in driveway base is 1.85 cubic yards, about 3.4 tons. The 1 in bedding sand layer is 0.31 cubic yards, about 0.42 tons. A 12 by 16 ft patio therefore needs about 4.4 tons of base before waste and about 0.8 tons of sand before joint sand.
Those tonnages are about a third higher than the answer from a gravel tool that prices loose stone at 1.4 tons per cubic yard when you type in the compacted volume. Stone is bought loose and ends up denser once a plate compactor has finished with it, so the cubic yards on the truck and the cubic yards in the hole are different numbers. This guide works every quantity from published unit weights and the paver industry's own layer specification, and shows where each figure is a published value and where it is a planning assumption.
What the paver industry specifies for each layer
The Concrete Masonry & Hardscapes Association (CMHA) publishes Tech Note PAV-TEC-002-22, Construction of Interlocking Concrete Pavements, revised 2022. Four passages set the quantities in everything that follows. The first fixes the base thickness:
"The thickness of the base is determined by traffic, soil type, subgrade soil drainage and moisture, and climate. Sidewalks, patios and pedestrian areas should have a minimum base thickness (after compaction) of 4 in. (100 mm) over well-drained soils. Residential driveways on well-drained soils should be at least 6 in. (150 mm) thick. In colder climates, continually wet or weak soils will require that bases be thicker."
For ordering, that paragraph matters in two ways. The thickness is measured after compaction, so the quantity is a compacted volume. And 4 in and 6 in are minimums on well-drained soil, not defaults for every yard: a clay yard in a freezing climate calls for more, and the quantities below scale linearly with thickness, at 0.57 tons per inch of depth per 100 square feet.
The second passage fixes the bedding sand and says what it cannot do:
"Bedding sand should be spread and screeded to an uncompacted nominal 1 in. (25 mm) thickness. Frozen or saturated sand should not be installed. If there is an uneven base (due to inconsistent compaction or improper grading), the bedding sand should not be used to compensate for it. Over time, unevenness in the bedding sand will reflect through to the surface. Uneven areas on the base surface must be made even prior to placing the bedding sand."
The sand layer is specified before compaction, so the quantity is an uncompacted volume, the opposite convention from the base. The third passage limits what can be bought as bedding sand:
"Bedding sand under concrete pavers should conform to ASTM C33 or CSA A23.1. This material is often called concrete sand. Masonry sand for mortar should never be used for bedding, nor should limestone screenings or stone dust."
The same section adds that the sand should have symmetrical particles, "generally sharp, washed, with no foreign material", and that waste screenings and stone dust "often do not compact uniformly and can inhibit lateral drainage of moisture in the bedding layer." So a bag or pile sold as "paver sand" or "leveling sand" is only bedding sand if it meets ASTM C33 or CSA A23.1; the name alone does not say. The weights used below are for a clean concrete sand of that kind.
The fourth passage covers compaction of the base:
"Bases for pedestrian areas and residential driveways should be compacted a minimum 98% of standard Proctor density. For vehicular areas, compaction should be at least 98% of modified Proctor density as determined by ASTM D1557, or AASHTO T180. While the highest percentage compaction (100%) is preferred, it may not be achievable on weak or saturated soils."
The 98% figure is a density target, not a volume allowance. It does not mean "order 2% extra". It matters for the arithmetic only because the unit weights in the next section assume a base that has been compacted properly; a base left loose holds fewer tons per cubic yard and settles under the pavers.
Two more instructions from the same bulletin set the tolerance on how much material a real job absorbs. Lifts are specified as: "Spread and compact the base in 4 to 6 in. (100 to 150 mm) lifts using 7,000 lbf (31 kN) reversible plate compactors. Thinner lifts will be required for compactors in the 5,000 lbf (22 kN) range." And on thickness error: "Unless otherwise specified, the compacted thickness of individual lifts should be +3/4 in. to –1/2 in. (+19 mm to –13 mm)." The surface of the finished base is allowed to vary: "Variation in final base surface elevations should not exceed ±3/8 in. (± 10 mm) when tested with a 10 ft. (3 m) straightedge." Those tolerances explain why a sand order can land well above the textbook number.
Quantities per 100 square feet
The base volume is area times compacted thickness. One inch of depth over 100 square feet is 8.33 cubic feet, or 0.309 cubic yards. The formula in tons is:
where 324 is 12 inches per foot times 27 cubic feet per cubic yard. At the WSDOT planning value of 1.85 tons per compacted cubic yard, each inch of base over 100 square feet is 0.571 tons.
| Layer and depth | Cubic feet | Cubic yards (in place) | Tons at 1.70 | Tons at 1.85 | Tons at 1.90 | Loose cubic yards (truck measure) |
|---|---|---|---|---|---|---|
| Base 4 in (patio minimum) | 33.33 | 1.235 | 2.10 | 2.28 | 2.35 | 1.55 |
| Base 5 in | 41.67 | 1.543 | 2.62 | 2.85 | 2.93 | 1.94 |
| Base 6 in (driveway minimum) | 50.00 | 1.852 | 3.15 | 3.43 | 3.52 | 2.32 |
| Base 8 in | 66.67 | 2.469 | 4.20 | 4.57 | 4.69 | 3.10 |
| Base 10 in | 83.33 | 3.086 | 5.25 | 5.71 | 5.86 | 3.87 |
The loose-yards column multiplies the in-place volume by 1.254, the ratio of compacted to truck-measure weight for crushed surfacing base course (explained in the next section). Bedding sand follows a different table because its density, volume convention and moisture are different:
| Bedding sand, 1 in uncompacted, per 100 sq ft | Dry weight assumed | Cubic yards | Pounds | Tons |
|---|---|---|---|---|
| Lighter, loosely screeded | 90 lb/ft³ (1.22 T/cy) | 0.309 | 750 | 0.375 |
| Working value | 100 lb/ft³ (1.35 T/cy) | 0.309 | 833 | 0.417 |
| Heavier, well-graded | 105 lb/ft³ (1.42 T/cy) | 0.309 | 875 | 0.438 |
The sand densities are planning assumptions, bracketed by published limits explained below. They are dry weights; the weight on a delivery ticket includes water.
Where the weights come from
Crushed stone base
The Washington State Department of Transportation Design Manual (M 22-01.23, September 2024) includes, in Chapter 620, an estimating table headed "Unit Dry Weight - Gravel Base and Surfacing". It lists a truck-measure weight and a compacted-on-roadway weight for each material. For the two crushed surfacing courses that resemble a paver base:
| Material (WSDOT Exhibit 620-1) | Truck measure, lb/cy (T/cy) | Compacted on roadway, lb/cy (T/cy) |
|---|---|---|
| Crushed Surfacing Top Course | 2,850 (1.43) | 3,700 (1.85) |
| Crushed Surfacing Base Course | 2,950 (1.48) | 3,700 (1.85) |
| Gravel Base | not listed | 3,400 to 3,800 (1.70 to 1.90) |
| Permeable Ballast | not listed | 2,800 (1.40) |
The footnote on the Gravel Base row is the sentence the planning range comes from: "3,700 lb/cy (1.85 tons/cy) is recommended as the most suitable factor; however, if the grading approaches the coarseness of ballast, the factor would approach 3,800 lb/cy (1.90 tons/cy), and if the grading contains more than 45% sand, the factor would decrease, approaching 3,400 lb/cy (1.70 tons/cy) for material that is essentially all sand." A dense-graded base for pavers is the same kind of material as the base under asphalt, which is why CMHA says that "Specifications typically used by cities, states, or provinces for aggregate base materials under flexible asphalt pavements are adequate for interlocking concrete pavements." The table is a Washington State figure for Washington crushed rock, so treat 1.85 as the best published planning value and not as a measurement of the pile in your supplier's yard. The supplier's scale ticket is the real number.
Reading the two columns together gives the compaction allowance. A cubic yard of crushed surfacing base course measured in the truck weighs 2,950 lb; a cubic yard of the same stone compacted in place weighs 3,700 lb. Stone that fills one cubic yard in the hole therefore took 3,700 / 2,950 = 1.254 cubic yards of truck measure to deliver, or 1.298 for the top course (3,700 / 2,850). That is the source of the 25% to 30% loose-to-compacted allowance. It applies to a purchase by volume. It does not apply on top of a tonnage that already uses 1.85, because the tons are the same either way: 1.235 compacted cubic yards at 1.85 tons is 2.28 tons, and 1.55 truck-measure cubic yards at 1.48 tons is also 2.28 tons.
Open-graded stone behaves differently. WSDOT lists permeable ballast at 2,800 lb per compacted cubic yard (1.40 tons), 24% lighter than dense-graded base. Single-size washed stone, such as the No. 57 stone CMHA specifies around drain pipes, is open-graded too, so its weight per yard is closer to the permeable ballast row than to the dense-graded rows. Dense-graded material is what the paver industry describes for the base proper, and its weight is what the tables above use.
Bedding sand
The WSDOT footnote above gives one sand figure: 1.70 tons per compacted cubic yard (3,400 lb, or 126 lb/ft³) for a material that is "essentially all sand". That is a compacted, dry value for road base. Bedding sand is placed loose and screeded, and CMHA specifies its thickness uncompacted, so the weight that governs the order is the loose weight.
The Federal Highway Administration's Soils and Foundations Reference Manual, Volume I (FHWA NHI-06-088, December 2006) tabulates void ratios and normalized dry unit weights for granular soils in Table 5-4, citing Kulhawy and Mayne (1990). Multiplying the table's normalized values by the unit weight of water the table gives, 62.4 lb/ft³:
| Table 5-4 soil type | Dry unit weight, loosest state | Dry unit weight, densest state |
|---|---|---|
| Clean, uniform sand | 1.33 × 62.4 = 83 lb/ft³ (1.12 T/cy) | 1.89 × 62.4 = 118 lb/ft³ (1.59 T/cy) |
| Clean, fine to coarse sand | 1.36 × 62.4 = 85 lb/ft³ (1.15 T/cy) | 2.21 × 62.4 = 138 lb/ft³ (1.86 T/cy) |
Those are the loosest and densest states in the table, the maximum and minimum void ratios. Screeded bedding sand starts near the loose end and the plate compactor then moves it toward the dense end. The working value of 100 lb/ft³ (1.35 tons per cubic yard) used in this guide is an assumption inside that range, with 90 to 105 lb/ft³ as the bracket. It also matches the 1.35 tons per cubic yard that the sand calculator applies. The check against the other published number is consistent: the compacted all-sand value of 126 lb/ft³ is 1.26 times the 100 lb/ft³ working value, almost the same loose-to-compacted ratio WSDOT's table gives for stone (1.25).
The sand calculator's own reference lists mason sand at about 1.5 tons per cubic yard, 11% above the working value here. CMHA excludes masonry sand for mortar from bedding use, so a quote for mason sand, or for a sand with no stated specification, is the first thing to question. The same bulletin accepts a sand meeting ASTM C144 or CSA A179 for filling the joints, so a mason sand sold as meeting one of those standards can serve as joint sand, though not as bedding.
Water and rock type
WSDOT states that "Weights shown are dry weights and corrections are required for water contents." The notes give two corrections, to be applied in order: scale the tabulated weight by the material's specific gravity divided by 2.65, then multiply by one plus the water content. Stockpiled sand and stone are often damp, and the delivery ticket weighs the water too. As an illustration (not a typical figure), 4% water on the 4.39 tons of base for the patio below adds 0.18 tons, and 8% adds 0.35 tons. A stone with a specific gravity of 2.70 in place of 2.65 weighs 1.9% more, which is 0.08 tons on the same base. Neither correction changes the thickness of the layer; they change how many tons you are charged for to fill it.
Compacted yards, loose yards and tons are three different orders
A base is specified in compacted inches. A truck delivers loose stone. A supplier sells either by weight or by volume. That makes three separate quantities for the same job, and a mistake in which one you are quoting is the common source of a short or long delivery.
If the supplier sells by the ton, use the compacted volume times 1.85 (or the supplier's own compacted factor), add waste, and order tons. No separate loose-to-compacted factor is needed.
If the supplier sells by the cubic yard, convert to truck measure by multiplying the compacted volume by 1.25 to 1.30, WSDOT's ratios for base course and top course. For the patio base below that turns 2.37 compacted yards into 2.97 to 3.08 loose yards before waste.
If you are using a calculator, find out what density it assumes. The gravel calculator takes a volume in cubic feet and returns tons at 1.4 tons per cubic yard, a loose-stone weight close to WSDOT's truck-measure column (1.43 to 1.48). It reports 3.32 tons for the 64 cubic feet of a compacted 4 in patio base, against 4.39 tons at WSDOT's compacted weight, a shortfall of 24.3%. Two ways to use the tool correctly for a compacted base: multiply the compacted cubic feet by 1.32 (that is 1.85 divided by 1.4) before typing them in, or multiply the tons it returns by 1.32. Either reproduces the 1.85 figure. For bedding sand no adjustment is needed, because the sand layer is specified uncompacted and the calculator's 1.35 tons per cubic yard equals the 100 lb/ft³ working value.
What moves the numbers more than the nominal depth
The textbook quantities assume a base of exactly 4 in or 6 in and a flat, perfect surface. The tolerances CMHA allows show how far a real job drifts.
On the base, a lift allowed to be 3/4 in thick is 19% more stone on a 4 in patio and 12.5% more on a 6 in driveway; a lift 1/2 in thin is 12.5% less on the patio and 8.3% less on the driveway. Per 100 square feet, a 4 in base of 2.28 tons becomes 2.00 tons at the thin limit and 2.71 tons at the thick limit. The CMHA wording is "unless otherwise specified", so a local engineering standard can be tighter, but the order should leave room for the high side.
On the sand, the same allowance has a bigger effect because the layer is thin. CMHA allows the finished base surface to vary ±3/8 in, and it forbids using the sand to fix that variation. A base that sits 3/8 in low over the whole area would hold 1 3/8 in of sand instead of 1 in, 37.5% more. The sand quantity is therefore the least predictable item in the order, and the arithmetic should be read as a range rather than a point: the nominal 1 in layer is 0.417 tons per 100 square feet, and the bounding case of a uniformly low base is 0.573 tons.
The slope requirement has a similar effect on the base. CMHA instructs: "Slopes should be a minimum of 1.5%. In the case of roads, the minimum longitudinal slope should be 1% with a minimum cross slope of 2%." Over a 12 ft run, 1.5% is a drop of 2.16 in; over 16 ft it is 2.88 in. If the subgrade is dug flat and the surface is tilted by feathering the base, the 4 in minimum has to be held at the thin end, so the average thickness is 1.08 in more across 12 ft, or 5.08 in on a 4 in base: 27% more stone. Over 16 ft the average is 5.44 in, 36% more. Digging the subgrade to the same slope as the finished surface keeps the thickness uniform and the quantity at the nominal value. The decision about where to put the slope is made at excavation, and it changes the order by a quarter or more.
Excavation depth follows from the layers. Concrete pavers for patios and driveways are specified as 2 3/8 in (60 mm) thick, so a patio is dug to 4 + 1 + 2.375 = 7.375 in below the finished surface, and a driveway to 6 + 1 + 2.375 = 9.375 in. Those depths are before any extra thickness for wet or weak soil.
Worked example: a 12 by 16 ft patio
Inputs: 192 square feet, a 4 in compacted base, 1 in of uncompacted bedding sand, 2 3/8 in pavers, well-drained soil, a subgrade cut to the finished slope. Excavation. 192 sq ft × 7.375 in is 118.0 cubic feet in the bank, or 4.37 cubic yards of soil to remove and haul, before the volume gain when dug soil loosens.
Base. The compacted volume is 192 × 4 / 12 = 64.0 cubic feet, or 2.370 cubic yards.
| Basis | Tons | Notes |
|---|---|---|
| Compacted weight 1.70 T/cy | 4.03 | Sandier or finer grading |
| Compacted weight 1.85 T/cy | 4.39 | WSDOT recommended factor |
| Compacted weight 1.90 T/cy | 4.50 | Coarse grading |
| 1.85 with 4% water on the ticket | 4.56 | Illustrative water content |
| 1.85 plus 10% waste | 4.82 | Stockpile allowance below |
| Gravel calculator on 64 ft³ at 1.4 T/cy | 3.32 | Under-reports by 24.3% |
| Base 3/4 in thick across the job | 5.21 | CMHA tolerance, high side |
| Base 1/2 in thin across the job | 3.84 | CMHA tolerance, low side |
Base order. Start from 4.39 tons and add 10%, which WSDOT's note provides for material that is stockpiled ("If material is to be stockpiled, increase required quantities by 10% to allow for waste."). A delivery dumped on the driveway and moved to the excavation by wheelbarrow is stockpiled in the sense that matters, since some stone stays under the pile or leaves with the wheelbarrow runs. That makes 4.82 tons. The order of 5 tons covers it with 0.18 tons to spare, 14% over the no-waste figure.
If the supplier sells by volume instead, the loose volume is 2.370 × 1.254 = 2.97 cubic yards (3.08 at the top-course ratio), and 3.27 with the 10% on the base-course ratio. That rounds to 4 yards, which at 2,950 lb per truck-measure yard is 5.9 tons of stone. Rounding up to the next whole yard here buys about 0.9 tons more than rounding 4.82 tons up to the next half ton. If the quote is only in whole yards, 3 yards is 4.42 tons by weight, within 1% of the no-waste requirement and with nothing left for a thick lift, so the choice is between 3 yards and a short base or 4 yards and a surplus of about a ton.
Bedding sand. The nominal layer is 192 × 1 / 12 = 16.0 cubic feet, or 0.593 cubic yards. At 90, 100 and 105 lb/ft³ that is 0.72, 0.80 and 0.84 tons. If the base surface turns out to be 3/8 in low everywhere, the layer is 1.375 in and the quantity rises to 1.10 tons at 100 lb/ft³. Add joint sand (about 172 lb, or 0.09 tons, for the smallest the joints can be: see the joint section below) and the sand total is 0.89 tons at nominal and 1.19 tons at the bounding case.
A sensible order for this patio is therefore 5 tons of base and 1 to 1.25 tons of sand. The sand is the item to size to the quality of the base work: with a screeded, string-checked base, 1 ton covers it with a margin; with a base that is only roughly graded, the extra quarter-ton is cheap insurance, and CMHA's instruction not to level the base with sand means the alternative of correcting the base is the better use of the time.
Worked example: a 20 by 12 ft driveway apron
Inputs: 240 square feet, a 6 in compacted base for a residential driveway over well-drained soil, 1 in of uncompacted sand, 2 3/8 in pavers. This is the area at the end of a driveway where it meets the street. Where the apron crosses the public right-of-way, the municipality's standard governs, and CMHA's own figure for streets is higher: "Minimum base thicknesses for residential streets are 8 to 10 in. (200 to 250 mm)."
Excavation. 240 sq ft × 9.375 in is 187.5 cubic feet, or 6.94 cubic yards in the bank.
Base. The compacted volume is 120.0 cubic feet, or 4.444 cubic yards.
| Basis | Tons | Notes |
|---|---|---|
| Compacted weight 1.70 T/cy | 7.56 | Sandier or finer grading |
| Compacted weight 1.85 T/cy | 8.22 | WSDOT recommended factor |
| Compacted weight 1.90 T/cy | 8.44 | Coarse grading |
| 1.85 plus 10% waste | 9.04 | Stockpile allowance |
| Gravel calculator on 120 ft³ at 1.4 T/cy | 6.22 | Under-reports by 24.3% |
| Base 3/4 in thick across the job | 9.25 | CMHA tolerance, high side |
| Base 1/2 in thin across the job | 7.54 | CMHA tolerance, low side |
With waste the requirement is 9.04 tons. Ordering to the next half ton gives 9.5 tons (15.5% over the no-waste figure), and ordering to the next whole ton gives 10 tons (21.6% over). Sold by volume, 4.444 × 1.254 × 1.10 is 6.13 truck-measure cubic yards, which rounds to 7 yards, or 10.3 tons at 2,950 lb per yard. In this case the three routes converge on 9.5 to 10.3 tons, and the margin is worth having on a 6 in base. CMHA's lift range is 4 to 6 in for a 7,000 lbf plate compactor, and "Thinner lifts will be required" for a 5,000 lbf machine, so a rented compactor in the lighter class means thinner lifts, for example two 3 in lifts of 4.11 tons each in place of one 6 in lift.
The compaction target is the same as for the patio. CMHA groups "pedestrian areas and residential driveways" at 98% of standard Proctor density, and reserves the modified Proctor figure for "vehicular areas". Whether a particular driveway counts as one or the other is a judgment for whoever designs it. Neither changes the tonnage; the choice changes how thorough the compaction must be.
Bedding sand. The nominal layer is 20.0 cubic feet, or 0.741 cubic yards: 0.90, 1.00 and 1.05 tons at 90, 100 and 105 lb/ft³. If the base is 3/8 in low throughout the layer is 1 3/8 in and the quantity is 1.38 tons at 100 lb/ft³ (1.44 tons at 105). Joint sand adds 0.11 tons, giving a total of 1.11 tons nominal and 1.48 tons bounding. An order of 1.5 tons covers every case. At about a ton and a half, the sand is a small load, so ask whether the supplier has a minimum delivery weight or charge before assuming that a half ton is the unit.
Rounding the order
Three kinds of rounding apply, and they stack.
Waste comes first. WSDOT's 10% is a published allowance for stockpiled material. It is not a loss rate for neat work; on a job where the delivery is dumped next to the excavation and the crew spreads directly, the real loss is lower, and on a job where the pile sits on a lawn or a gravel drive it is higher. Treat the 10% as the working figure when you have no better one.
Sales increments come second. Suppliers sell in increments that vary by yard and by product, such as a half ton, a whole ton or a whole cubic yard, and many have a minimum delivery. The examples above round to the nearest half ton and whole ton because those are common, but the increment for your order is the supplier's. Ask whether the quote is by weight or by volume, whether the volume is measured in the truck or by weight conversion, and whether the weight is dry or as-delivered. The same stone is 3,700 lb per compacted cubic yard in the hole, 2,950 in the truck, and heavier when wet.
What happens to the surplus comes third. Bedding sand has a second use on the same job, because CMHA says it can also fill the joints, so a sand order that runs long is less wasteful than a stone order that runs long. When a project has no second use for the stone, the order can be tighter on stone and looser on sand, because sand is the quantity most exposed to base tolerances.
Rounding once, at the end, matters more than rounding at each step. Rounding the patio base of 4.39 tons up to 5, adding 10% to reach 5.5 and rounding again orders 6 tons, a full ton more than rounding 4.82 tons once to 5. Carry the unrounded figures through the whole calculation and round only the number you give the supplier.
Joint sand, paver count and the drainage option
Joint sand is a separate small item. CMHA specifies joints "between 1/16 and 3/16 in. (2 and 5 mm)", and the sand is swept into them and vibrated down. Its volume is the fraction of the paved area that is joint times the paver thickness. For 4 by 8 in units, each joint width gives:
| Joint width | Units per 100 sq ft | Joint share of area | Joint sand per 100 sq ft (100 lb/ft³) |
|---|---|---|---|
| 1/16 in | 439.6 | 2.30% | 46 lb |
| 1/8 in | 429.7 | 4.52% | 90 lb |
| 3/16 in | 420.0 | 6.67% | 132 lb |
On the 192 sq ft patio, that is 825 pavers and 172 lb of joint sand at 1/8 in joints; on the 240 sq ft apron, 1,031 pavers and 215 lb. These are geometry-only values with no cut allowance, and the joint sand figure is the void volume, which is the minimum. The bulletin says the bedding sand "also can be used to fill the joints, but it may require extra effort in spreading and compacting", so one product for both is workable. For a separate joint sand, CMHA writes: "Joint sand may be finer than the bedding sand to facilitate filling of the joints like a sand meeting ASTM C144 or CSA A179 requirements."
The brick calculator counts units across a length-by-height area, but its smallest joint setting is 1/4 in, wider than the paver range; for 4 by 8 in units that gives 410.7 per 100 sq ft instead of 429.7 at 1/8 in, 4.4% low. It suits brick-sized edging but not a full paver field. For the cut pavers along the edges, the paver border cut waste calculator separates field units from perimeter units and applies cut and breakage allowances. CMHA's instruction for the edge is that "Cut pavers should be used to fill gaps along the edge of the pavement" and that "Gaps greater than 3/8 in. (10 mm) should be filled with cut pavers."
The optional drainage line is another stone quantity that people leave out. In clay or other slow-draining soils under vehicle loads, CMHA describes "Typical 4 in. (100 mm) diameter perforated drainage pipes surrounded with minimum 3 in. (75 mm) of No. 57 or similar open-graded stone", wrapped in geotextile, "placed along the pavement perimeter". Around the 56 ft perimeter of the 12 by 16 patio, a trench 10 in wide and 10 in tall (an assumed section: 4 in pipe plus 3 in of stone on each side and above and below, ignoring the pipe's own volume) holds 38.9 cubic feet, or 1.44 cubic yards. At WSDOT's 1.40 tons per cubic yard for open-graded permeable ballast, the nearest published row, that is about 2.0 tons, almost half the weight of the patio's base. The bulletin ties drain pipes to "clay soils or other slow draining soils subject to vehicular traffic", so the quantity is an add-on for those sites and not part of the standard order.
Where these figures stop applying
The tables assume the soil is well drained and the climate is not severe. CMHA says "In colder climates, continually wet or weak soils will require that bases be thicker", and for streets it points to engineering rather than a rule of thumb: "A qualified civil engineer familiar with local soils and traffic conditions should be consulted to determine the appropriate base thickness for streets and heavy-duty, industrial pavements." The 8 to 10 in figures in the table above are the bulletin's minimum for residential streets, listed to show how the quantity scales, not as advice to build a street.
Two more limits come from the sources themselves. The stone weights are dry, planning-level values for Washington State crushed surfacing and the sand weights are a bracket for clean concrete sand, so a particular quarry's product will differ, and the ticket weight decides what you pay for. The 4 in and 6 in thicknesses are minimums for a pedestrian patio and a residential driveway, and a manufacturer's installation instructions, a local code or a soils report takes precedence over this guide. The gravel and sand calculators linked here are volume-to-weight converters. They are not design tools, and no calculator can say whether the subgrade is stable.
Once the quantities are fixed, the same measure-first logic carries to the concrete for a slab edge or footing in how many bags of concrete you need, and to the planting bed next to the patio in how much new mulch to add over old mulch. The homeowners hub lists the other material guides.
Sources
- Concrete Masonry & Hardscapes Association (CMHA), PAV-TEC-002-22, Construction of Interlocking Concrete Pavements, revised 2022: base thickness, bedding sand, compaction, lifts, tolerances, slope, joint widths, drainage pipe and joint sand. Quotes are from the text of the web edition; fractions render as "23/8" in that edition and are shown here as 2 3/8. Tables 4 to 6 of the bulletin (gradations) are not used. Checked November 3, 2026.
- Washington State Department of Transportation, Design Manual M 22-01.23, Chapter 620, Exhibit 620-1, "Unit Dry Weight - Gravel Base and Surfacing", September 2024 (M 22-01.23 is the latest edition listed on WSDOT's Design Manual index): truck-measure and compacted weights, grading footnote, specific gravity and water content corrections, 10% stockpile allowance. Checked November 3, 2026.
- Federal Highway Administration, Soils and Foundations Reference Manual, Volume I (FHWA NHI-06-088), December 2006, Table 5-4 (after Kulhawy and Mayne, 1990): void ratios and normalized dry unit weights for clean sands; unit weight of water 62.4 lb/ft³. Checked November 3, 2026.
- Planning assumptions, not published values: the 100 lb/ft³ working dry weight of bedding sand (bracket 90 to 105 lb/ft³), the example water contents of 4% and 8%, the 20 by 12 ft apron and 12 by 16 ft patio dimensions, the supplier rounding increments, and the 4 by 8 in paver size. Loose-to-compacted ratios, tonnages, volumes, paver counts and joint sand volumes are computed by CalculatorVillage from the sources above.