Ratio Calculator

Simplify a ratio to its lowest terms, solve a proportion for a missing value, or split a total according to a ratio — switch tabs for whichever one you need.

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Leave C blank for a two-term ratio (A:B), or fill it in for a three-term ratio (A:B:C).
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Leave exactly one of the four boxes blank — that's the one this solves for.
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Multiplies every term in the ratio by the scale factor — e.g. 2:3 scaled by 4 becomes 8:12.
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Splits the total into parts proportional to the ratio — e.g. split $100 in a 2:3 ratio to get $40 and $60.
Result Live
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Fraction Calculator

Simplifying a ratio

Method
Divide every term by their greatest common divisor (GCD)   Example: 8:12 — GCD is 4 — simplifies to 2:3

This is the same idea as simplifying a fraction, just applied to two or more numbers at once. A ratio like 100:250:50 simplifies to 2:5:1 — every term divided by the same number (50, their GCD) without changing the underlying proportion. Decimal ratios work the same way; the calculator clears the decimal point first, then reduces normally.

Solving a proportion

Method
A:B = C:D — cross-multiply to solve for whichever term is missing   Example: 2:5 = 6:? — solve D = (5 × 6) ÷ 2 = 15

A proportion is just two equal ratios. If you know three of the four numbers, the fourth is fixed — there's exactly one value that keeps both sides proportional, found by cross-multiplying and solving. This is the classic "solve for x" ratio problem: enter three values and leave the one you don't know blank.

Dividing a total by a ratio

Method
Each part = (that term ÷ sum of all terms) × total   Example: split 100 in a 2:3 ratio — parts are 40 and 60

Useful whenever a fixed amount needs to be split proportionally — splitting a bill or profit share unevenly by agreement, mixing ingredients to a target batch size, or dividing a budget across categories by a set ratio.

Frequently asked questions

How do you simplify a ratio?

Divide every term in the ratio by their greatest common divisor (GCD). 8:12 has a GCD of 4, so it simplifies to 2:3 — the same proportion, written with smaller numbers.

How do you solve a ratio for an unknown value?

Set up a proportion (A:B = C:D) with the unknown in one position, then cross-multiply and solve. For 2:5 = 6:?, the missing value is (5 × 6) ÷ 2 = 15.

How do you split a number into a ratio?

Divide the total by the sum of the ratio's terms, then multiply that result by each term individually. Splitting 100 in a 2:3 ratio: the sum is 5, so each "part" is worth 20, giving 40 and 60.