Proportion Calculator

Name: Proportion Calculator
Author: Jitendra Kumar

Solve missing values in proportions, compare equivalent ratios, and scale ratios with cross multiplication.

Last Updated: April 26, 2026

Solve missing term

Find x in A / B = C / D with cross multiplication.

Missing Term

A (left numerator)

B (left denominator)

C (right numerator)

Leave this term blank or enter any value; it will be solved.

D (right denominator)

Main Result

Left Ratio

Right Ratio

Cross Products

0 = 0

Important Disclaimer

This calculator provides estimates for informational purposes only and does not constitute tax, legal, or financial advice. Tax laws are complex and change frequently. Consult a qualified tax professional for advice specific to your situation. CalculatorWallah is not responsible for any decisions made based on calculator results.

Reviewed For Methodology, Labels, And Sources

Every CalculatorWallah calculator is published with visible update labeling, linked source references, and founder-led review of formula clarity on trust-sensitive topics. Use results as planning support, then verify institution-, policy-, or jurisdiction-specific rules where they apply.

Reviewed By

Jitendra Kumar, Founder & Editorial Standards Lead, oversees methodology standards and trust-sensitive publishing decisions.

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Topic Ownership

Sales tax and tax-sensitive estimate tools, Education and GPA planning calculators, Health, protein, and screening-formula pages, Platform-wide publishing standards and methodology

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Methodology & Updates

Page updated April 26, 2026. Trust-critical pages are reviewed when official rates or rules change. Evergreen calculator guides are checked on a recurring quarterly or annual cycle depending on topic volatility.

Sources & methodology About the review process

How to Use the Proportion Calculator

Step 1: Choose a mode
Pick Solve missing term, Compare ratios, or Scale a ratio depending on the task.
Step 2: Enter the ratio values
For A / B = C / D, enter the known terms and select the missing term if solving for x.
Step 3: Calculate the proportion
The calculator uses cross multiplication and displays the key ratio values and cross products.
Step 4: Review the steps
For missing-value problems, use the step list to see how the equation was rearranged.

How Cross Multiplication Works

A proportion states that two ratios are equal. In the standard setup A / B = C / D, the cross products must match: A x D = B x C. That rule lets the calculator solve for any missing term by rearranging the equation.

For example, if 3 / 4 = x / 20, then the right numerator is missing. The calculator rearranges the proportion as x = (3 x 20) / 4, giving x = 15.

The compare mode uses the same cross-product test. If A x D equals B x C, the two ratios are proportional. The scale mode uses a scale factor to multiply both terms of a ratio by the same amount, preserving the relationship.

Proportion Calculator Guide

What Is A Proportion?

A proportion is an equation that says two ratios are equal. That makes proportions useful for scaling recipes, reading maps, resizing images, comparing rates, and solving algebra problems where one value is unknown.

Proportions are closely related to fractions and percentages. If you need exact fraction arithmetic first, use the fraction calculator. If you want a part-to-whole result as a percent, use the percentage calculator.

Task	Formula	When to use it
Solve A in A / B = C / D	A = (B x C) / D	Use when the left numerator is missing
Solve B in A / B = C / D	B = (A x D) / C	Use when the left denominator is missing
Solve C in A / B = C / D	C = (A x D) / B	Use when the right numerator is missing
Solve D in A / B = C / D	D = (B x C) / A	Use when the right denominator is missing
Check a proportion	A x D = B x C	If cross products match, the ratios are proportional

Proportion Examples

Worked examples make the cross-multiplication pattern easier to trust. The calculator keeps the cross products visible so you can verify whether the result really preserves the original ratio.

Example	Setup	Result
3 / 4 = x / 20	x = (3 x 20) / 4	x = 15
5 / 8 = 15 / 24	5 x 24 = 8 x 15	120 = 120, so the ratios are proportional
16 : 9 scaled to width 1920	Scale factor = 1920 / 16	Scaled ratio is 1920 : 1080
2 / 7 = 10 / x	x = (7 x 10) / 2	x = 35

Common Uses

Proportion problems appear in practical work whenever one quantity must stay in the same relationship to another. Aspect ratios, map scales, rates, recipes, and unit comparisons are all proportion problems once the numbers are set up correctly.

Use case	How proportions help
Classroom algebra	Solve for x in proportion equations and show the cross-multiplication path
Recipes and mixtures	Scale ingredients while preserving the same ratio
Maps and scale drawings	Translate from a drawing measurement to a real-world measurement
Aspect ratios	Resize images, screens, and videos without stretching
Rates and unit comparisons	Check whether two rates describe the same proportional relationship

Mistakes To Avoid

The most common proportion mistakes are setup mistakes. Confirm which values belong in the numerator and denominator before calculating, and convert units first when the two ratios use different measurement systems.

Mistake	Fix
Cross multiplying the wrong terms	In A / B = C / D, multiply A x D and B x C
Allowing a zero denominator	A denominator of zero makes the ratio undefined
Rounding too early	Keep full precision until the final result, especially for repeated scaling
Comparing unlike units	Convert units first when one ratio uses inches and the other uses centimeters
Confusing ratio with percent	A ratio can be converted to a percent, but the setup must still use the correct base

Keep the research moving with Percentage Calculator, Fraction Calculator, Slope Calculator, and Scientific Calculator.