Ratio Calculator
Simplify ratios, solve A : B = C : D for a missing value, scale a ratio and divide a total by a ratio.
Simplify a ratio
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Solve a proportion (A : B = C : D)
Leave one box empty — its value is worked out for you.
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Scale a ratio
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Divide a total by a ratio
How it works
Four ratio calculators on one page, all updating as you type. Simplify a ratio reduces A : B to its lowest terms by dividing both sides by their greatest common divisor — 6 : 8 becomes 3 : 4. Decimals are handled too: they are first scaled up to whole numbers (0.5 : 0.75 becomes 50 : 75, then 2 : 3). Alongside the simplified form you also get the ratio as a decimal, in 1 : n form, and as percentages of the total, which is the quickest way to turn a ratio into a percentage.
Solve a proportion fills in the missing value of A : B = C : D by cross multiplying, so 3 : 4 = 9 : ? gives 12 — this is the classic "solve for x" ratio problem. Scale a ratio multiplies both sides by the same factor (use a value below 1 to shrink), and Divide a total by a ratio shares an amount out in any number of parts: 1000 in 2 : 3 : 5 is 200, 300 and 500. Every calculation runs in JavaScript inside your browser — nothing is uploaded, there is no sign-up and there are no ads.
Frequently asked questions
How do you simplify a ratio?
Divide both sides by their greatest common divisor. For 6 : 8 the largest number that divides both is 2, so the simplified ratio is 3 : 4. Decimal ratios are scaled up to whole numbers first — 0.5 : 0.75 becomes 50 : 75 and then 2 : 3. Type your two values into the Simplify a ratio box and the lowest-terms answer appears instantly, together with the ratio as a decimal, in 1 : n form and as percentages of the total.
How do I solve for x in a ratio or proportion?
Cross multiply: in A : B = C : D the products A × D and B × C are equal, so any missing value is the product of the two known opposite numbers divided by the remaining one. In the Solve a proportion box, fill in three of the four fields and leave the unknown one empty — 3 : 4 = 9 : ? gives 12. It works for any position, so you can solve for A, B, C or D.
How do you divide a number into a ratio?
Add the parts of the ratio to get the total number of shares, divide the amount by that total, then multiply by each part. Sharing 1000 in the ratio 2 : 3 : 5 means 10 shares of 100, giving 200, 300 and 500. Enter the total and a ratio like 2:3:5 in the Divide a total by a ratio box and each share is listed with its percentage — it accepts any number of parts.