Ratio Calculator

What is ratio calculator?

A ratio compares two quantities, such as 16 to 9 for a widescreen display. Simplifying a ratio puts it in its lowest terms, which makes patterns easy to see.

If you know one real value, the tool also scales the ratio. For example, if the width of a screen is 1920 pixels, it finds the height.

How to use the ratio calculator

1. Enter the two parts of the ratio.
2. Enter a known value to scale the ratio, if you want.
3. Read the simplified ratio and the scaled values.

How the ratio calculator works

For whole numbers, both parts are divided by their greatest common divisor. The decimal is A divided by B. If a value C stands for A, the matching B is B times C divided by A. If C stands for B, the matching A is A times C divided by B.

Worked example

Common uses of the ratio calculator

• Resizing images and videos.
• Scaling recipes.
• Reading map scales.
• Mixing paint or concrete.
• Homework on proportions.

Tips and common mistakes

Keep units the same on both sides of the ratio.

For recipes, scale every ingredient by the same factor.

Background: what to know before you rely on it

Ratios appear everywhere: recipes, maps, screens, gear systems, finance and mixes. They are unitless comparisons, so 2 to 1 is the same ratio whether it is cups or kilograms. The rule of three is the everyday method for solving proportions: multiply across the known pair and divide by the third number. Take care to keep the order. The ratio A to B is not the same as B to A, and mixing them up is the most common mistake.

Private, free and fast

This tool runs entirely in your browser. What you type or choose is not uploaded to a server and is not saved after you close the page, which keeps it fast and private. It is free to use as often as you like. See more in all calculators, or browse the full list of tools.

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Results are for information and education. For legal, financial, medical or security decisions, check with a qualified professional. Financial results are estimates and exclude fees and taxes unless the tool says otherwise.