Ratio Calculator – Simplify Ratios to Lowest Terms
Use this free ratio calculator to reduce any two numbers to their simplest whole-number ratio. Enter both values; the tool finds the GCD and divides both sides to give you the lowest equivalent form—useful for recipes, map scales, mixing and proportions. No sign-up, runs in your browser.
Ratio Calculator
Enter two positive numbers to reduce the ratio to simplest whole-number form.
How the ratio calculator works
A ratio a:b is in simplest form when a and b have no common factor other than 1. The calculator finds the greatest common divisor (GCD) of a and b and divides both by it:
simplified_a = a ÷ GCD(a, b), simplified_b = b ÷ GCD(a, b)
For example, 12 and 18 have GCD 6, so 12:18 becomes 2:3. The GCD is found using the Euclidean algorithm (repeated division). The result keeps the same proportion but in the smallest whole numbers.
When and why to use a ratio calculator
A ratio describes how two quantities relate—for example, 3 parts flour to 2 parts sugar, or 1 cm on a map representing 50,000 cm on the ground. Working with ratios often means simplifying them to the smallest whole numbers so they are easier to compare, scale or communicate. A ratio calculator does that in one step: you enter the two values and get the simplified form. No need to find the GCD by hand or worry about arithmetic errors.
Ratios appear in many everyday situations. In cooking, a recipe might call for flour and water in a 5:2 ratio—if you scale up or down, you need that proportion. In mixing paint, concrete or garden fertiliser, instructions often give ratios. Map scales (1:50000, 1:100000) are ratios: 1 unit on the map equals that many units on the ground. Financial ratios, screen aspect ratios and dilution problems all use the same idea. A simplified ratio makes it clear: 18:12 and 3:2 express the same relationship, but 3:2 is easier to use.
Ratios are related to percentages and proportions. If a mix is 2:3, the first part is 2/(2+3) = 40% of the total. When you need to convert a ratio to a percentage or work out "what percent is X of Y," use our percentage calculator. When you need to simplify or scale a ratio, use this ratio calculator. For sale prices and discounts, the discount calculator helps. Together these tools cover many everyday math tasks.
The calculator runs entirely in your browser and does not store your inputs. You can use it on a shared or work device without leaving data on a server. Enter positive whole numbers; the tool returns the simplified ratio in whole numbers. If your quantities are decimals, multiply both by a power of 10 to make them integers first, then simplify.