Ratio Calculator
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Simplify a ratio to its lowest terms, or find the missing number in a proportion.
- Type the two sides of the ratio
- Leave the third box empty to simplify
- Fill it in to solve for the missing number
About this tool
Two jobs that are the same arithmetic pointed different ways. Simplify: 1920:1080 is 16:9. Solve: if 16:9 and the width is 1280, the height is 720. Decimals are handled properly, which is less common than it should be. A ratio of 2.5:1 simplified by rounding first becomes 3:1 — a different ratio. Here both sides are scaled to whole numbers before anything is reduced, so 2.5:1 comes back as 5:2, which is the same ratio written correctly. When you solve for a missing number it is not forced to be whole. 16:9 at a width of 1000 is 562.5, and there is no honest way to round that without saying so: video encoders round to even numbers, print rounds to whatever the paper is, and those are decisions belonging to whoever asked. So the tool tells you when the answer did not come out whole rather than quietly tidying it. Useful for aspect ratios, scale drawings, mixing ratios, map scales and recipe scaling. It runs in your browser and nothing is sent anywhere.
Frequently asked questions
How do I work out an aspect ratio?
Put the width and height in as the two sides. 1920 and 1080 simplify to 16:9; 2560 and 1080 to 64:27, which is the honest answer for an ultrawide even though nobody calls it that. The simplified pair is the ratio, whatever the original numbers were.
Can I use decimals?
Yes, and they are handled properly. Both sides are scaled up to whole numbers before being reduced, so 2.5:1 becomes 5:2 rather than being rounded to 3:1. Rounding first changes the ratio, which is the whole thing you are trying to preserve.
Why is the answer not a whole number?
Because it genuinely is not. 16:9 at 1000 pixels wide is 562.5 high. Which way you round depends on what it is for — video usually wants an even number, print does not care — so the tool says the answer was not whole and leaves the decision to you.
How do I scale a recipe?
Use the solve mode: put the original quantity and the original servings as the ratio, then the servings you want as the third number. The answer is the new quantity. Do it once per ingredient, or once and multiply, since the factor is the same for all of them.
Why can't a side be zero?
Because nothing is in proportion to zero, and simplifying would mean dividing by it. A ratio needs two real quantities to compare; if one of them is nothing, there is no ratio to express.
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