Calculators

Ratio Calculator

Simplify a ratio to lowest terms, or find the missing number in a proportion such as 16 : 9 = 1280 : ?

How it works

To simplify, divide both sides by g, their greatest common divisor. Decimals are first scaled by a power of ten until both sides are whole numbers, so 1.5 : 2.25 becomes 150 : 225 and then 2 : 3. To complete a proportion, cross-multiply: if A : B = C : ?, the missing value is C × B ÷ A.

A : B = A÷g : B÷g | ? = C × B ÷ A
g
Greatest common divisor of A and B
1 : n
The ratio scaled so the first part is 1
Shares
Each side as a percentage of A + B

Worked example

A 1920 × 1080 screen, and the height that keeps the same shape at 1280 pixels wide.

  1. 1Greatest common divisor of 1920 and 1080: 120
  2. 21920 ÷ 120 : 1080 ÷ 120 = 16 : 9
  3. 3Missing height: 1280 × 1080 ÷ 1920 = 720

The ratio is 16 : 9, and a 1280-pixel-wide version is 720 pixels tall.

Frequently asked questions

How do I split an amount in a ratio?

Add the parts, divide the amount by the total, and multiply by each part. To split ₹1,000 in the ratio 2 : 3, each part is worth 1,000 ÷ 5 = 200, so the shares are 400 and 600. The calculator's shares figure gives the same split as percentages.

Can ratios have decimals?

Yes, but they are usually written in whole numbers. The calculator multiplies both sides by 10, 100 and so on until they are whole, then simplifies, so 0.75 : 1.25 becomes 3 : 5.

What is the difference between a ratio and a fraction?

A ratio compares parts with each other; a fraction compares a part with the whole. In a class of 12 girls and 18 boys the ratio is 2 : 3, and girls are 2/5 of the class.

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