Ratio Calculator
Solve a proportion or reduce a ratio. Enter three of the four values in A:B = C:D and leave one blank to find the missing term, or simplify any ratio to its lowest terms.
How to use the ratio calculator
- Pick a mode: solve a proportion or simplify a ratio.
- Enter your numbers, leaving exactly one field blank when solving a proportion.
- Read the answer, which updates as you type.
Examples
Solve for the missing term
1 : 2 = ? : 10
? = 5, because 1 / 2 equals 5 / 10
Simplify a screen ratio
1920 : 1080
16 : 9
Frequently asked questions
What is a ratio and what is a proportion?
A ratio compares two quantities, such as 3:2. A proportion states that two ratios are equal, such as 3:2 = 6:4. This tool both solves proportions and reduces ratios.
How does it solve for the missing value?
It uses cross multiplication. For A:B = C:D the products A times D and B times C are equal, so any single missing term can be found by rearranging that equation.
How do I simplify a ratio to lowest terms?
Divide both sides by their greatest common divisor. For example 4:8 has a common divisor of 4, so it reduces to 1:2. The calculator does this automatically.
Can I use it to scale a recipe or mixture?
Yes. Set up a proportion like 2:3 = x:9 to scale ingredients up or down, or keep a fixed ratio while changing the total amount of a mixture.
Why am I getting an error?
When solving a proportion you must leave exactly one field blank. The calculator also reports an error if the answer would require dividing by zero.
Is my data sent anywhere?
No. Every calculation runs locally in your browser, so the numbers you enter never leave your device.
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