Proportion Calculator

Find a missing value when two ratios are proportional. Enter your own values below to see missing value X and check the method behind it.

All calculators

Your inputs

Change the example values to match your situation.

Your result

Let’s work it out.

Fill in your inputs and select Calculate.
Your result and breakdown will appear here.

How this calculator works

For A:B = C:X, X = B × C ÷ A.

KEEP EXPLORING

View category
Basic CalculatorScientific CalculatorPercentage CalculatorPercentage Change CalculatorPercentage Difference CalculatorFraction Calculator

What is Proportion Calculator?

Proportion Calculator helps you find a missing value when two ratios are proportional.

The main result is missing value X. The formula, example and assumptions below explain how to interpret it.

How to use Proportion Calculator

Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.

  1. Gather a in A:B = C:X, b in A:B = C:X and c in A:B = C:X. Use values from the same situation or reporting period.
  2. Replace the example a in A:B = C:X with your own value, then complete the other fields. Check the displayed units.
  3. Select Calculate and read missing value X. Change one input and calculate again to compare a second scenario. Reset restores the original example.
  • Enter a in A:B = C:X, at least 0. Decimals are accepted.
  • Enter b in A:B = C:X, at least 0. Decimals are accepted.
  • Enter c in A:B = C:X, at least 0. Decimals are accepted.

Proportion Calculator: a worked example

With the inputs below, the result is 15 (missing value X). Follow the example, then replace these illustrative values with your own.

Example inputs and output
Input or outputExample value
A in A:B = C:X2
B in A:B = C:X3
C in A:B = C:X10
Missing value X15

Understanding the Proportion result

The main output is missing value X. It applies to the inputs and operation you selected.

Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.

Proportion Calculator: assumptions and common mistakes

A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.

  • Check the base value, sample definition and chosen operation. Display rounding should come after the calculation.

For wider guidance, visit NIST statistical handbook. The formula and scope of this specific tool are stated on this page.

Proportion Calculator FAQs

What does Proportion Calculator calculate?

Proportion Calculator helps you find a missing value when two ratios are proportional. Its main output is missing value X.

What inputs do I need for Proportion Calculator?

You need a in A:B = C:X, b in A:B = C:X and c in A:B = C:X. Use the field labels and units to match your figures to the formula.

Which formula does Proportion Calculator use?

For A:B = C:X, X = B × C ÷ A.

What is a worked example for Proportion Calculator?

Example inputs: A in A:B = C:X: 2; B in A:B = C:X: 3; C in A:B = C:X: 10. The result is 15 (missing value X).

How should I enter a in A:B = C:X?

Enter a in A:B = C:X, at least 0. Decimals are accepted.

How do I choose b in A:B = C:X?

Enter b in A:B = C:X, at least 0. Decimals are accepted. The example uses 3; replace it if your circumstances differ.

How should I read missing value X?

The main output is missing value X. It applies to the inputs and operation you selected.

Why might my Proportion Calculator result differ from my records?

Check the base value, sample definition and chosen operation. Display rounding should come after the calculation. Differences in entered values, units or rounding can also change the comparison.

Can I compare two scenarios in Proportion Calculator?

Yes. Note your first missing value X, change a in A:B = C:X or another input, and select Calculate again. Editing a field clears the old result so it is not mistaken for a new calculation.

Is Proportion Calculator free, and where are my inputs calculated?

This calculator is free to use without signing in. Its formula runs in your browser; calculator inputs are not sent to a calculation API. The inputs reset to the example values when you reset the form or start a fresh page.