Ratio Calculator
Simplify a ratio to its lowest terms and scale it to any size — both directions.
Simplify a ratio
Find a missing value
How to use
- Enter the two numbers of your ratio (A and B). The simplified ratio and its decimal form appear instantly.
- To solve a proportion, type a new value for A — the matching B is calculated, and vice versa.
- Decimals work too: 2.5 : 1.5 simplifies to 5 : 3.
Examples
Simplify 1920:1080
Type 1920 and 1080 — the simplified ratio is 16 : 9, or 1.7778 : 1 as a decimal.
Recipe scaling
A recipe uses flour and sugar at 3 : 2. If you have 450 g of sugar (B), the proportion gives 675 g of flour (A).
FAQ
How is a ratio simplified?
Both numbers are divided by their greatest common divisor (GCD). For 1920:1080 the GCD is 120, giving 16:9.
Can I use decimal numbers in a ratio?
Yes. Decimals are scaled up to whole numbers first (2.5:1.5 becomes 25:15), then simplified as usual to 5:3.
How does the missing-value (proportion) calculation work?
It solves A : B = newA : newB by cross-multiplying. Given 16:9 and a new A of 1280, newB = 1280 × 9 ÷ 16 = 720.
Why are zero or negative numbers rejected?
A ratio compares two positive quantities; with a zero or negative side the comparison (and division) stops being meaningful, so the tool asks for positive numbers.