Simplify a ratio to lowest terms, or find a missing term in an equivalent ratio.

How to Use the Ratio Calculator

Toggle between simplifying a ratio and solving for a missing term in an equivalent one — the second mode needs one extra field the first doesn't.

Ratios and fractions share their math but not their meaning — a ratio compares two separate quantities (3 cups flour to 1 cup sugar), while a fraction is a piece of one whole (3/4 of a pizza). Both simplify the same way, dividing through by the greatest common factor:

a : b  →  (a ÷ gcf) : (b ÷ gcf)

8:12 becomes 2:3, since 4 divides evenly into both. This Ratio Calculator also solves the other common problem: finding a missing term in an equivalent ratio. Two ratios are equivalent exactly when their cross-products match — a:b = c:d means a×d = b×c — so rearranging for an unknown gives x = (b × c) ÷ a. If 2:5 = 6:x, then x = 30 ÷ 2 = 15.