General Calculators
Ratio Calculator
Simplify ratios and solve proportions such as 2:5 = 8:X with clear formulas.
Calculator
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Result
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Formula
To simplify a:b, divide both terms by their highest common factor.
For a proportion a:b = c:d, the cross products are equal: a × d = b × c. The missing term is d = (b × c) ÷ a when a is not zero.
Solved example
A small plaster mix is quoted as 12 parts sand to 18 parts gravel. Highest common factor of 12 and 18 is 6.
12 ÷ 6 = 2 and 18 ÷ 6 = 3, so the ratio is 2:3.
If you keep that ratio and use 8 parts sand, gravel = (3 × 8) ÷ 2 = 12 parts.
Frequently asked questions
What is 12:18 in simplest form?
Divide both sides by 6. The simplest ratio is 2:3.
How do I find the missing term in 2:3 = 8:d?
Cross-multiply: 2 × d = 3 × 8 = 24, so d = 12. The proportion is 2:3 = 8:12.
Is a ratio the same as a percentage?
No. 2:3 means two shares against three shares. The first share is 2/5 of the whole, which is 40%, but only after you add the parts to get the whole.
Can both terms be zero?
No. 0:0 does not describe a mix, so the calculator will not simplify it.