Math & Statistics
Ratio and Proportion Solver
Solve a:b = c:d for a missing fourth value and compare the two ratios directly. The calculator uses if a ÷ b = c ÷ d, then d = b × c ÷ a. It returns more than one result so you can check the main answer against a useful secondary measure. Equivalent ratios have equal cross-products. A zero denominator makes a ratio undefined, even if software can display a large or infinite value.
Check the displayed units, assumptions, and rounding before relying on the result.
Calculate and compare
Use the number box for precision or the slider for fast scenario testing.
Scenario results
Missing value d
20
Completes a:b = c:d.
First ratio a/b
0.6
Decimal form.
Cross-product check
60 = 60
Equal cross-products confirm the proportion.
How the calculation works
Use consistent units and retain full precision until the final display step.
Worked example
Reproduce the displayed scenario, then change one assumption at a time.
Assumptions behind the result
- • Inputs use the units shown beside each control.
- • The displayed formula is applied without hidden market or demographic data.
- • Rounding occurs only for display; calculations keep full numeric precision.
- • Equivalent ratios have equal cross-products.
- • A zero denominator makes a ratio undefined, even if software can display a large or infinite value.
Mistakes that change the answer
- • Mixing percentages with decimals or mixing incompatible units.
- • Relying on a rounded intermediate value instead of the full result.
- • Changing several assumptions at once instead of testing ratio value a separately.