Ratio calculator

This ratio calculator simplifies a ratio to the smallest whole numbers, solves a proportion or splits an amount in a given ratio. 12 : 8 : 6 simplifies to 6 : 4 : 3; 260 split in the ratio 12 : 8 : 6 gives 120, 80 and 60.

Source: Wikipedia – Ratio: simplifying, equivalent ratios, proportion. Updated: 6 October 2026.

What do you want to do?

a (first value)

b (second value)

c (third value, 0 = leave out)

In a proportion: leave the value you are looking for empty or enter 0.

More parts (optional)

For ratios with more than three numbers when simplifying, splitting and scaling, separated by colons.

My ToolboxYour inputs are saved in this browser only.

Result

Result: 12 : 8 : 6 = 6 : 4 : 3
Conversion: Scaled to 1: 1 : 0.6667 : 0.5
Shares: Share of a: 46.15%
Share of b: 30.77%
Share of c: 23.08%
As a fraction, decimal and percent
Step by step: 12 ÷ 2 = 6, 8 ÷ 2 = 4, 6 ÷ 2 = 3
= 6 : 4 : 3
Calculation: Greatest common divisor: 2 – divide all numbers by 2

How it is calculated

Simplifying a ratio

A ratio a : b stays the same if you multiply or divide both numbers by the same amount. To simplify it, divide by the greatest common divisor (GCD). Decimals are first multiplied by 10, 100 … to get whole numbers.

12 : 8 : 6 = 6 : 4 : 3 (GCD 2)
15 : 10 = 3 : 2
1.5 : 2.5 = 15 : 25 = 3 : 5

Solving a proportion

For a : b = c : x the product of the means equals the product of the extremes, so x = b × c ÷ a. Example: a recipe for 4 people needs 300 g of flour – for 6 people, 4 : 300 = 6 : x, so x = 450 g. The rule of three works on the same principle.

Splitting an amount in a ratio

Each part gets total × part ÷ sum of the parts. A profit of 600 split 3 : 2 gives 360 and 240. The shares in percent are listed below.

Ratio, fraction and percent

A ratio of 3 : 2 can also be written as shares: 3 of 5 parts is 60%, 2 of 5 is 40%. Scaled to 1, it reads 1 : 0.67.

Honest limits

The calculator works with positive numbers and up to six decimal places. For mixtures (such as a 1 : 10 dilution) it matters whether the ratio refers to the parts or to the total volume – the instructions of the product decide that.

Find a missing value, check and scale

Any missing value: in a : b = c : d, leave the field you are looking for empty. 4 : b = 6 : 450 gives b = 4 × 450 ÷ 6 = 300.
Check: if all four values are filled in, the calculator compares the products a · d and b · c. 2 : 3 = 4 : 6 holds because 2 · 6 = 3 · 4 = 12.
Scale: every number is multiplied by the same factor. 2 : 3 with factor 2.5 gives 5 : 7.5 – useful for recipes, mixtures and map scales.
Fraction, decimal, percent: for two numbers, simplifying also shows every notation: 3 : 4 is the fraction 3/4, the decimal 0.75 and 75%.
More than three parts: enter the remaining numbers under “More parts”. 100 in the ratio 1 : 2 : 3 : 4 gives 10, 20, 30 and 40.

Frequently asked questions

How do I calculate a ratio?

Divide both numbers by their greatest common divisor: 12 : 8 has a GCD of 4 and simplifies to 3 : 2.

How do I calculate a ratio with 3 numbers?

The same way: divide all three numbers by their common GCD. 12 : 8 : 6 divided by 2 gives 6 : 4 : 3.

How do I solve a : b = c : x?

With x = b × c ÷ a. Example: 4 : 300 = 6 : x gives x = 300 × 6 ÷ 4 = 450.

How do I split an amount in the ratio 3 : 2?

Add the parts (5), divide the amount by 5 and multiply by 3 and 2. 600 gives 360 and 240.

How do I convert a ratio to percent?

Divide the part by the sum of the parts and multiply by 100: for 3 : 2 that is 3 ÷ 5 = 60% and 40%.

How do I find a missing value in a ratio?

Write the proportion a : b = c : d and leave the unknown field empty. The rule is a · d = b · c. Example: 4 : b = 6 : 450 gives b = 4 × 450 ÷ 6 = 300.

Sources and legal basis

As of: 6 October 2026 · Editorial policy