Helpful Toolbox

Ratio Calculator

Simplify any ratio to its lowest terms, or solve a proportion for the missing value — all right here in your browser.

📖 How it works & FAQ

Simplify a ratio

Enter two numbers to reduce A:B to its lowest terms.

:

Solve a proportion

Fill three boxes in A : B = C : X and leave one blank to solve for it.

: = :

What this ratio calculator does

A ratio compares two quantities, like 4:6 cups of flour to sugar or 16:9 for a screen. This tool does the two jobs you reach for most. First, it simplifies a ratio by dividing both sides by their greatest common divisor (GCD), so 4:6 becomes 2:3 — the same relationship in the smallest whole numbers. Second, it solves a proportion: when you know that A:B equals C:X and one value is missing, it cross-multiplies to find it. Decimals are welcome; the simplifier scales them to whole numbers before reducing.

Simplifying vs. solving

Use the top box when you just want a messy ratio boiled down to lowest terms. Use the proportion box when you are scaling something up or down — doubling a recipe, resizing an image, converting a map distance, or working out a mixture. Cross-multiplication means A:B = C:X is the same as A times X equals B times C, and the calculator rearranges that to isolate whichever box you left blank.

How to use it

  1. To reduce a ratio, type your two numbers into the A and B boxes under "Simplify a ratio." The lowest-terms result updates as you type.
  2. To solve a proportion, fill in three of the four boxes in A : B = C : X.
  3. Leave exactly one box empty — that is the value you want to find.
  4. Press Solve (or Enter). The answer and the completed proportion appear below.
  5. Hit Clear to reset the proportion and start over.

FAQ

Can I use decimals or negative numbers?
Yes. Decimals are scaled to whole numbers before simplifying, and negatives work in proportions. Results round to six decimal places for readability.
Which box should I leave blank?
Any one of the four. Solve for A, B, C, or X — just make sure the other three are filled and only one is empty.
Why do I get a "divide by zero" message?
Solving for a missing value requires dividing by a known number. If the number opposite your blank is zero, the proportion has no finite solution.
Is my data sent anywhere?
No. Every calculation runs in your browser. Nothing you type is uploaded or stored.