Ratio Calculator
Solve and scale ratios.
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About Ratio Calculator
The Ratio Calculator solves proportions and simplifies ratios in one place. Enter three values of A : B = C : D and leave one box blank to find the missing number, or switch to simplify mode to reduce any ratio to its lowest whole-number terms with its decimal value and percentage.
It is completely free with no sign-up, no limits, and no ads getting in the way. Every calculation runs instantly in your browser as you type, so your numbers are never sent to a server or stored anywhere.
Frequently asked questions
- How do I solve a proportion with this calculator?
- Choose the 'Solve a proportion' mode, then type any three of the four values in A : B = C : D and leave exactly one box blank. The calculator cross-multiplies for you and fills in the missing value instantly, along with the completed ratio.
- How does simplifying a ratio work?
- Switch to 'Simplify a ratio' mode and enter both terms. The tool divides both by their greatest common divisor to reduce the ratio to its simplest whole-number form, and also shows the decimal value, percentage, and the equivalent n : 1 and 1 : n forms. Decimal inputs like 2.5 : 5 are scaled to whole numbers automatically.
- Can it handle decimals and large numbers?
- Yes. Both the proportion solver and the simplifier accept decimals and large values. When simplifying decimals, the calculator scales the terms up to whole numbers before reducing, so you still get a clean whole-number ratio.
- What happens if I enter a zero or leave the wrong number of boxes blank?
- It handles these gracefully instead of showing an error like NaN. If solving would require dividing by zero, it tells you which value is the problem. If you leave more than one box blank, it reminds you to leave exactly one, and empty inputs simply wait for your numbers.
- Is the Ratio Calculator free to use?
- Yes, it is 100% free with no account, no subscription, and no usage limits. Use it as many times as you like.
- Is my data uploaded or stored anywhere?
- No. All calculations happen locally in your browser using JavaScript. Nothing you type is uploaded, tracked, or saved, so your numbers stay completely private.