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Proportion Calculator

Enter your values below to get the result first, then scroll for the full explanation and guidance.

Step 1 • Add values

Use the calculator

Enter your values below to generate an instant result. You can update the inputs at any time to compare different scenarios.

Example verified by the calculator's ratios and proportion reference cases.

Results refresh instantly as values change.

Missing fourth value

20a : b = c : d

Missing fourth value: 20 (a : b = c : d)

Cross-multiplication gives d = (b x c) / a.

Proportion result

Cross-multiplication gives d = (b x c) / a.

Result snapshot

A quick visual read of the values behind this result.

First ratio2 : 5
Second ratio8 : 20

Recommended next checks

  • →Keep quantities in compatible units before applying the proportion.
First ratio
2 : 5
Second ratio
8 : 20

Try different values to compare results.

Solve the missing fourth value in the proportion a : b = c : d.

Fast to use

Built for comparison

Clear result output

Table of Contents

6

About Proportion Calculator

Proportion Calculator helps you work through the main numbers for this topic quickly with a simple input flow and an instant result.

Use the calculator result as a practical starting point, then review the explanation and assumptions on the page if you want more context.

Calculation method

Cross-multiply to calculate d = (b x c) / a.

Formula explained

Calculation flow

This calculator is structured for fast UK-focused estimates with clear inputs, repeatable logic, and instant results.

Formula

Input values -> calculation engine -> instant result

How the result is built

1Enter the values requested in the form.
2The calculator applies the configured formula logic.
3The result updates instantly with a breakdown.
4Use the output to compare scenarios quickly.

Example

Example verified by the calculator's ratios and proportion reference cases.

Assumptions

  • Three finite real values where a is not zero and units are compatible.

Source basis

  • UK-focused calculator flow
  • Structured input validation
  • Instant result breakdowns

FAQ

Common questions

Three finite real values where a is not zero and units are compatible.

Trust and notes

Assumptions and important notes

This calculator is designed to give a fast estimate using the method shown on the page. Results are most useful when your inputs are accurate and the tool matches your situation.

Use the result as guidance rather than a final diagnosis or professional decision. If the result could affect health, legal, financial, or compliance decisions, verify it with a qualified source where appropriate.

  • Three finite real values where a is not zero and units are compatible.

Method

UK calculator guidance

Last reviewed

April 17, 2026