Simplify a ratio to lowest terms, and solve a proportion A : B = C : ? for the missing number.
Ratios are simplified by dividing both terms by their greatest common divisor. Non-integer inputs are rounded for the GCD. General information only.
A ratio simplifies by dividing both sides by their greatest common divisor — 8:12 becomes 2:3. A proportion scales it: if A:B holds and you know C, the missing term is B×C÷A.
Simplify: divide both by GCD · Solve A:B = C:? → ? = B×C ÷ A
Two equal ratios. If a recipe is 2:3 and you scale the first part to 20, the second scales to 30 to keep the same proportion.
Yes for the decimal and proportion outputs; the simplified whole-number ratio rounds inputs first.
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Yes. The Ratio Calculator is completely free, runs in your browser, and never asks for a signup, email, or download. Enter your numbers and the result updates instantly.
It uses standard formulas and recalculates the moment you change a value, so the math is exact for the inputs you enter. Treat the result as a reliable planning estimate; for decisions with legal or tax consequences, confirm the figures with a qualified professional.
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Last reviewed: September 2026. Free to use, no signup — Ratio Calculator by ToolWise Digital.
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