Method
How to calculate missing value d
The two ratios are set equal and cross-multiplied. A must be non-zero, since dividing by it is what isolates the missing value.
FORMULAD = (B × C) ÷ A
Worked example
Ratio calculator example
For 3 : 4 = 12 : D, the missing value is 16, and A is 42.9% of A + B.
Change one assumption at a time to see what drives the result. The output is an estimate, not a quote, forecast or recommendation.
FAQ
Ratio calculator FAQ
What if A is zero?
The proportion cannot be solved, because isolating D requires dividing by A.
Can I scale a recipe or mixture with this?
Yes. Enter the original two quantities as A and B, the new amount of the first as C, and D gives the matching amount of the second.
Does this simplify a ratio?
Not to whole numbers. It reports A : B as a decimal and as a percentage split, which is usually more directly comparable.