A ratio compares quantities, like 18:24. To simplify it, divide every term by the greatest common divisor (GCD) of all the terms — exactly like reducing a fraction. This calculator returns the simplest form, the GCD used, the decimal value and the 1:n form, for two- or three-term ratios.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: exact GCD reduction, recomputed in code.
How to simplify
The GCD is the largest whole number that divides every term. For 18 and 24 it's 6, so both shrink to 3 and 4. A ratio is in lowest terms once the GCD of its terms is 1 — nothing divides them all further. The same logic extends to three terms: take the GCD of all three and divide each by it.
Worked examples
18:24:
1920:1080 (screen ratio):
6:9:15 (three terms):
As a decimal, 18:24 is 0.75 (18 ÷ 24), and in 1:n form it's 1:1.33. These views are handy when scaling recipes, mixing ratios, or setting up a screen or print aspect ratio.
Frequently Asked Questions
Divide every term by the GCD of all terms. 18:24 ÷ 6 = 3:4.
16:9 — GCD is 120. The widescreen aspect ratio.
Yes. 6:9:15 ÷ GCD 3 = 2:3:5.
When the terms' GCD is 1 — no common factor left.
For two terms, yes — a:b is a/b, both reduce by the same GCD.