Math & Algebra Tool

Proportion Calculator

Solve for the missing value in a proportion A/B = C/D.

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Σ The Formula

A/B = C/D → Cross-multiply to solve for unknown

Real World Examples

Simple Proportion
1/2 = x/4 → x=2
Recipe Scaling
2 cups/4 servings = x cups/10 servings
Currency
1 USD / 0.9 EUR = 100 USD / x EUR
Map Scale
1 cm / 50 km = 3.5 cm / x km

# About This Calculator

A Proportion is an equation stating that two ratios or fractions are equal. It is often written as A/B = C/D or A:B :: C:D.

Proportions are the mathematical backbone of scaling. Whether you are adjusting ingredients for a larger party, calculating currency exchange rates, or working with map scales, you are using proportions.

Cross-Multiplication Principle: If A/B = C/D, then A × D = B × C. This allows you to easily find any single missing value if you know the other three.

How To Use

  1. Enter values for three of the fields (A, B, C, or D).
  2. Leave the field you want to find empty.
  3. Click Calculate.
  4. The missing value will be computed automatically.

Frequently Asked Questions

What is the detailed cross-multiplication formula?+

To solve for A: (B×C)/D. For B: (A×D)/C. For C: (A×D)/B. For D: (B×C)/A.

Can I use decimals?+

Yes, this calculator supports integers, decimals, and creates precise floating-point results.

What is a 'Direct' proportion?+

As one amount increases, another amount increases at the same rate. (e.g., buying more apples costs more money).

What is an 'Inverse' proportion?+

As one amount increases, the other decreases. (e.g., more workers usually means less time to complete a job). This tool solves Direct proportions.

Why do I get 'Infinity'?+

You likely divided by zero (e.g., having B=0 or C=0 in the denominator position). Proportions require non-zero denominators.

Is Proportion Calculator free to use?+

Yes, Proportion Calculator on Matheric is completely free to use. We believe in accessible education and utility for everyone.

About

A Proportion is an equation stating that two ratios or fractions are equal. It is often written as A/B = C/D or A:B :: C:D.

Proportions are the mathematical backbone of scaling. Whether you are adjusting ingredients for a larger party, calculating currency exchange rates, or working with map scales, you are using proportions.

Cross-Multiplication Principle: If A/B = C/D, then A × D = B × C. This allows you to easily find any single missing value if you know the other three.

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