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Ratio Calculator

Solve a proportion, simplify a ratio or split an amount, all on one page.

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Solve a proportion (A : B = C : D)

Leave exactly one of the four boxes empty.

:=:
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Simplify a ratio

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  • First term as 1-
  • Last term as 1-
  • Share of each term-

Split by ratio

PartRatioShareAmount

How to use

  1. In a proportion the product of the outer terms equals the product of the inner terms (A × D = B × C), which gives the missing value.
  2. Leave one of the four proportion boxes empty to see its value and the working. It is handy for resizing images or scaling a recipe.
  3. “Simplify a ratio” divides by the greatest common divisor to give the smallest whole-number ratio. Decimal ratios such as 1.5:2.25 are converted too.
  4. In “Split by ratio”, enter an amount and a ratio to get each share. Pick a rounding option and leftover units go to the largest remainders so the shares add up exactly.

FAQ

What aspect ratio is 1920 × 1080?

Dividing both by their greatest common divisor, 120, gives 16:9. Type 1920:1080 into “Simplify a ratio” to check.

Can I use ratios with three or more terms?

Yes. Type something like 2:3:5 and both simplifying and splitting work with every term.

Why do my split amounts not add up exactly?

With “Exact”, long decimals are rounded for display, so the visible numbers may be off by a little. Choose whole numbers or 2 decimal places and the leftover is handed out so the shares add up to the original amount.

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