Power Calculators

⚖️ Proportion Calculator

Solve a direct proportion a:b = c:d by calculating the missing fourth value from three known values.

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Fill in the details and click Calculate to see your results.


Also available in our Android app, with charts and full breakdown tables.

📘 About the Proportion

A proportion states that two ratios are equal.

This calculator solves a:b = c:d for the fourth value when A, B and C are known.

🧮 Formula

Proportion
a/b = c/d
Cross multiplication
a × d = b × c
Solve for d
d = b × c ÷ a

Where

  • a = first term
  • b = second term
  • c = third term
  • d = missing fourth term
This is a direct proportion. A must be non-zero for the displayed solution.

✏️ Worked example

2:3 = 4:d

You enter
A2
B3
C4
You get
Missing D6
A ÷ B Ratio0.666667

The missing value is 6.

Try this example →

🧭 How to use this calculator

What you enter

  • A
  • B
  • C

What you get

  • Missing D
  • A ÷ B Ratio

💡 Common uses

  • Scaling quantities.
  • Unit-rate and recipe problems.
  • Map and drawing scale calculations.
  • School mathematics problems involving equivalent ratios.

❓ Frequently asked questions

What is a proportion?

A proportion states that two ratios are equal.

How is the missing value found?

Cross multiplication gives a times d equals b times c, so d equals b times c divided by a.

Is this calculator for inverse proportion?

No. This calculator solves a direct proportion.