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Ratio Calculator

What do you want to do
Leave the one you want worked out empty
: = :
Any one of the four can be the empty one.

Fill in the ratio you have and press Calculate. The answer and the working behind it will show up here.

— —
Working out
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Solve a proportion, simplify, or scale a ratio

Solve for a missing value in A : B = C : D, reduce a ratio to its simplest whole-number form (decimals included), or scale a ratio up or down by a factor — with a visual bar showing how the two parts split.

How to use

  1. Pick proportion, simplify, or scale
  2. Enter the known values (leave one box blank for proportion mode)
  3. Read the result, the working, and the visual split of the ratio

Common questions

In the proportion mode, why do I have to leave exactly one box empty?

The tool solves A : B = C : D for whichever single value is unknown — with two unknowns there'd be no unique answer, and with none unknown there'd be nothing to solve, so it explicitly asks for exactly one blank.

Does simplifying a ratio with decimals work correctly?

Yes — a ratio like 2.5 : 1.5 is scaled up to whole numbers first (25 : 15) before the greatest common factor is applied, then reduced, giving 5 : 3.

If I scale a ratio by a factor, does the relationship between the two parts change?

No — both parts are multiplied by the same factor, so the ratio's underlying shape (the decimal you get from dividing one part by the other) stays identical; only the absolute size of the two numbers changes.