Proportion Solver
In a proportion the cross products are equal, so the unknown is B × C ÷ A. 3:8 = 12:32.
Your numbers
Unknown
32
Result
2.667×
Formula
Unknown = B × Base ÷ A
This is the same maths you use to scale a recipe up for more people or enlarge a drawing.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| AThe first number of the ratio — the 2 in 2:3. | 3 | 0 and up |
| BThe second number of the ratio — the 3 in 2:3. | 8 | 0 and up |
| BaseThe value everything is measured against — the denominator. | 12 | 0 and up |
Step by step
Quick reference table
Results when only A changes and everything else stays put.
| A | Unknown | Result (×) |
|---|---|---|
| 1.5 | 64 | 5.333 |
| 2.25 | 42.667 | 3.556 |
| 3 | 32 | 2.667 |
| 4.5 | 21.333 | 1.778 |
| 6 | 16 | 1.333 |
What each result means
| Result | At default values |
|---|---|
| UnknownThe blank slot in the proportion — the value being solved for. | 32 |
| Result (×)What the formula gives back — the answer this page is for. | 2.667 |
Common mistakes
This is the same maths you use to scale a recipe up for more people or enlarge a drawing.
Glossary
- A
- The first number of the ratio — the 2 in 2:3.
- B
- The second number of the ratio — the 3 in 2:3.
- Base
- The value everything is measured against — the denominator.
- Unknown
- The blank slot in the proportion — the value being solved for.
- Result
- What the formula gives back — the answer this page is for.
Frequently asked questions
Q. How is Proportion Solver calculated?
Unknown = B × Base ÷ A — In a proportion the cross products are equal, so the unknown is B × C ÷ A. 3:8 = 12:32.
Q. Can you walk through an example?
With A 3, B 8, Base 12, the answer is Unknown 32.
Q. What do I need to enter?
Enter A, B, Base. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only A moves the answer to A 1.5 → Unknown 64 and A 6 → Unknown 16. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
This is the same maths you use to scale a recipe up for more people or enlarge a drawing.
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