Ratio calculator

How it works

Simplifying divides both sides by their greatest common divisor until they share no common factor, so 42:58 becomes 21:29. Scaling multiplies both sides by the factor and leaves the ratio in the same relationship, so 3:5 times 4 is 12:20. Solving a proportion uses the cross product: from a:b as c:x the missing value is x = b times c divided by a. Zero is refused in any position because a ratio with a zero side carries no relationship, and a zero scale factor would collapse the ratio to 0:0.

Worked example

The ratio 42:58 simplifies to 21:29 because both sides divide by 2. Scaling 3:5 by a factor of 4 gives 12:20, which still simplifies back to 3:5. Solving 3:5 = 18:x uses x = 5 times 18 divided by 3, so the missing value is 30 and the finished proportion reads 3:5 = 18:30.

Questions and answers