Ratio Calculator
Simplify a ratio to its lowest terms, and scale it proportionally to a new value — useful for recipes or scale drawings.
How to use the ratio calculator
- Enter A and B — the two numbers the ratio consists of.
- The calculator simplifies the ratio to its lowest terms automatically.
- To scale the ratio to a new size, enter what A equals in the "If A equals" field, and the corresponding value for B is calculated.
How ratios are calculated
A ratio A : B is simplified by dividing both numbers by their greatest common divisor (GCD):
To scale a ratio proportionally — that is, to find what B becomes if A changes to a new value C — use:
A common example is scaling a recipe: if a recipe for 4 people uses 6 dl of flour, and you're cooking for 10 people, the ratio is 4 : 6, and the amount of flour becomes 10 × (6 ÷ 4) = 15 dl. The same principle is used in map scales and drawings, where the ratio between distance on the map and actual distance stays constant.
Frequently asked questions
What is a ratio?
A ratio shows the relationship between two quantities, written as A : B. It tells you how many times larger or smaller one value is compared to the other, without saying anything about the actual sizes.
How do I simplify a ratio?
Divide both numbers in the ratio by their greatest common divisor (GCD). For example, 4 : 6 simplifies to 2 : 3 by dividing both numbers by 2.
How do I use ratios to scale a recipe or a drawing?
Set up the ratio between the two quantities (e.g. number of people and amount of ingredient), and scale proportionally: new amount = new value × (original amount ÷ original value). The same method is used for scale on maps and drawings.