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Proportion Calculator Online

Solve proportions instantly with our free proportion calculator. Enter three known values to find the missing value in A : B = C : D using accurate cross multiplication.

Use this proportion solver to solve ratios, find a missing value, calculate A, B, C or D, and verify your answer with clear step-by-step calculations.

Solve Proportions Cross Multiplication Find Missing Value Ratio & Proportion Step-by-Step Solution

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A:B

Solve Your Proportion

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Enter three values and find the missing value.

:
=
:
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Finding A

Enter B, C and D. The calculator will find A.

Quick Examples

What Is a Proportion Calculator?

A proportion calculator is an online tool used to solve equations where two ratios are equal. A common proportion is written as A : B = C : D. When one value is missing, the calculator can determine the unknown value using cross multiplication.

This proportion calculator online lets you solve for A, B, C or D. Enter three known values, select the missing value, and the calculator provides the answer together with the calculation steps and verification.

You can use this tool as a proportion solver, ratio calculator, or cross multiplication calculator for common mathematical proportion problems.

What Can This Proportion Calculator Calculate?

Solve different types of proportion problems with accurate calculations and clear step-by-step results.

Find Missing A

Find A when B, C and D are known using the proportion formula.

Find Missing B

Solve for B when the other three values are available.

Find Missing C

Calculate C from a complete proportion with one unknown value.

Find Missing D

Find the fourth value in a proportion using cross multiplication.

Cross Multiplication

Automatically applies cross multiplication to solve the selected missing value.

Decimal Proportions

Enter decimal values when solving proportions that are not limited to whole numbers.

Step-by-Step Solution

See the formula, calculation and substitution used to find the missing value.

Result Verification

Verify the completed proportion by comparing both cross-products.

Copy Results

Copy the completed proportion and calculation result with one click.

How to Use the Proportion Calculator

Solve a proportion in just a few simple steps.

1

Enter Three Values

Enter the three known values in your proportion A : B = C : D.

2

Select the Missing Value

Choose whether you want to find A, B, C or D.

3

View Your Solution

Click Solve Proportion to see the answer, formula, calculation and verification.

Proportion Formula & Cross Multiplication

A proportion states that two ratios are equal. For example, A : B = C : D. When written as fractions, this becomes A / B = C / D.

Main proportion formula:

A × D = B × C

Cross multiplication allows you to rearrange the equation and calculate whichever value is missing.

Find A

A = (B × C) ÷ D

Find B

B = (A × D) ÷ C

Find C

C = (A × D) ÷ B

Find D

D = (B × C) ÷ A

Common Uses for a Proportion Calculator

A proportion solver can be useful when you need to determine an unknown number from two equivalent ratios. It can help with basic math exercises, ratio problems, measurements and everyday calculations.

Students can use a cross multiplication calculator to check proportion exercises and understand how the missing value is calculated.

The calculator can also be used for proportional relationships where values contain decimals. Enter the known values and select the unknown value to receive the calculated result.

Important Information About Proportions

A valid proportion requires the relationship between the two ratios to be consistent. The calculator uses cross multiplication to determine the missing value and then verifies the completed proportion.

When solving a proportion, the denominator used in the relevant formula cannot be zero. Always check that the values you enter form a mathematically valid proportion.

Frequently Asked Questions About Proportions

What is a proportion?

A proportion is an equation showing that two ratios are equal. For example, 2 : 3 = 10 : 15 is a proportion.

How does a proportion calculator work?

Enter three known values, select the missing value, and the calculator applies the appropriate proportion formula using cross multiplication.

What is cross multiplication?

Cross multiplication multiplies opposite values in two equal fractions. For A/B = C/D, the resulting equation is A × D = B × C.

Can I find any missing value?

Yes. This proportion calculator can solve for A, B, C or D as long as the other three values are provided and the calculation is mathematically valid.

Can I use decimal values?

Yes. The calculator accepts decimal values and calculates the missing value from the entered proportion.

How can I verify a proportion?

Multiply the opposite values on both sides. If A × D equals B × C, the completed proportion is satisfied.

Is this proportion calculator free?

Yes. You can use this online proportion calculator to solve proportion problems without installing additional software.

What is the difference between a ratio and a proportion?

A ratio compares two quantities, while a proportion states that two ratios are equal. For example, 2 : 3 is a ratio, while 2 : 3 = 10 : 15 is a proportion.

Solve Your Proportion

Use our free proportion calculator to solve A : B = C : D, find missing values, apply cross multiplication, and check your result with step-by-step calculations.

Solve Proportion