Proportion Calculator

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Proportion Calculator

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Solve proportions instantly. Enter any three values in A/B = C/D to find the missing number with cross-multiplication steps.

Enter any three values and leave the value you want to find blank.

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About This Calculator

How to Solve a Proportion

For A/B = C/D, cross-multiply to get A × D = B × C. Divide by the number paired with the unknown. For example, 3/4 = 12/x becomes 3x = 48, so x = 16.

Proportion formulas

Missing value	Formula
A	A = (B × C) / D
B	B = (A × D) / C
C	C = (A × D) / B
D	D = (B × C) / A

Common uses

Proportions scale recipes, maps, drawings, unit rates, mixtures, similar figures, and percent problems. Always compare quantities in matching units before solving.

Calculation history

Your 10 most recent solved proportions will appear here and stay available on this device.

Frequently asked questions

What is a proportion?

A proportion is an equation stating that two ratios are equal, such as 3/4 = 12/16.

How do you solve a proportion?

Cross-multiply to form A × D = B × C, then divide both sides to isolate the missing value.

Can a proportion contain decimals or negative numbers?

Yes. The same cross-multiplication rule works for fractions, decimals, and negative values as long as no denominator is zero.

What is the difference between a ratio and a proportion?

A ratio compares two quantities. A proportion states that two ratios represent the same relationship.

How do I check a proportion answer?

Substitute the missing value, then compare the cross products. If A × D equals B × C, the two ratios form a valid proportion.

Can I solve percent proportions?

Yes. Write the percent as P/100 and set it equal to part/whole. For example, 20/100 = 30/x gives x = 150.

Does this proportion solver show steps?

Yes. It identifies the missing term, displays the cross-multiplication identity, substitutes your values, and shows the division used to isolate the answer.

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Proportion Calculator

Free proportion calculator. Enter any three values in A/B = C/D to find the missing number with instant cross-multiplication steps.