Ratio Calculator

A ratio compares two quantities, such as 3:2. A proportion is a statement that two ratios are equal, such as 3:2 = 6:4. The Simplify tab works on a single ratio, while the Solve tab works on a proportion where one term is unknown.

It uses cross multiplication. For A:B = C:D the products A times D and B times C are always equal, so the calculator rearranges that equation to isolate whichever term you left blank and divides to get the answer.

Switch to the Simplify tab and enter both numbers. It divides each side by their greatest common divisor. For example 1920 and 1080 share a divisor of 120, so the ratio reduces to 16:9.

Both fields accept decimals. Solve mode handles decimals cleanly through cross multiplication. Simplify mode is designed for whole numbers, since the greatest common divisor is defined for integers, so decimal input there may not reduce the way you expect.

Solve mode needs precisely one unknown. If you leave two or more boxes empty, or fill in all four, there is nothing single to solve for, so it asks you to supply three terms and clear just one.

Solving for a term requires dividing by one of the values you entered. If that divisor is zero, for example solving for D in 0:B = C:D, the result is undefined and the calculator reports the error instead of returning a wrong number.

Yes. Set up a proportion like 2:3 = x:9 to hold a fixed ratio while changing the total, then read the solved term. This is handy for scaling ingredients, paint mixes, fertilizer dilutions, or model measurements up and down.

Yes, any finite number works, including negatives. Cross multiplication is still valid, so a proportion like -2:4 = ?:10 solves to -5. Negative ratios rarely make physical sense, but the math is handled correctly.

No. Every calculation runs locally in your browser as you type, so the numbers you enter never leave your device and nothing is stored.