Ratio Calculator
Simplify ratios, find missing values and scale ratios instantly.
All calculations happen locally in your browser — nothing is uploaded, stored or tracked.
Pick a mode
Simplify a ratio, or solve for a missing value.
Enter the values
Both ratio parts, plus the third value in solve mode.
Read the result
Simplified or solved, with the working shown.
What Is a Ratio Calculator?
A ratio compares two quantities — for example, a paint mix of 2 parts blue to 1 part white (2:1). This calculator simplifies ratios to their lowest terms, finds a missing term when three of the four values are known, and scales a ratio by a given amount.
Ratios behave like fractions: 4:6 simplifies to 2:3 by dividing both sides by their greatest common divisor. The missing-value mode solves the proportion a:b = c:x, which is how you scale recipes, mixes and maps.
The Method
In simplify mode the calculator divides both parts by the GCD. In find-X mode it cross-multiplies to solve for the unknown. The result is always reduced to its simplest whole-number form where possible.
Your data never leaves your device.
Every calculation on this site runs in your browser using vanilla JavaScript. Nothing is uploaded, stored or tracked.
- 100% local, client-side calculations
- No data stored on any server
- No tracking, no analytics, no ads scripts
- Works offline once loaded
Frequently Asked Questions
How do I simplify a ratio?
Divide both parts by their greatest common divisor. 12:18 becomes 2:3.
How do I find x in a ratio?
If a:b = c:x, then x = (b × c) ÷ a. For 2:3 = 8:x, x = 24 ÷ 2 = 12.
What is the difference between a ratio and a fraction?
A fraction compares a part to the whole; a ratio compares two parts to each other, though the math is similar.
Can I scale a ratio?
Yes — enter the ratio and the new value of one part; the calculator finds the matching value of the other part.
Can ratios have decimals?
Yes. The calculator works with decimals and simplifies to whole numbers when possible.