Ratio Calculator
Simplify a ratio to its lowest terms.
Input sheet
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A ratio compares two quantities — parts of a recipe, an aspect ratio, a gear pairing, a mix of paint. Reducing it to lowest terms makes the relationship easy to read and easy to scale.
How it works
Divide both sides by their greatest common divisor.
Two ratios are equivalent when both sides share a common factor. Simplifying means dividing both numbers by their greatest common divisor (GCD) until nothing but 1 divides them both.
This tool rounds each input to a whole number first, then divides both sides by their GCD, so 18 : 24 and 3 : 4 describe exactly the same proportion.
Simplified ratio = (a ÷ GCD) : (b ÷ GCD), where GCD is the greatest common divisor of a and b
Worked examples
Simplifying the ratio 18 : 24. → 3 : 4
The GCD of 18 and 24 is 6; dividing both gives 3 : 4.
Reducing a 1920 : 1080 screen ratio. → 16 : 9
The GCD of 1920 and 1080 is 120, and 1920 ÷ 120 : 1080 ÷ 120 = 16 : 9.
Tips & gotchas
- To scale a recipe or mix, multiply both sides of the simplified ratio by the same number — 3 : 4 doubled is 6 : 8.
- A ratio of a : b can be read as a fraction a/b or split into a/(a+b) and b/(a+b) when you need each part's share of the whole.
- If your numbers have units, keep them consistent before simplifying — comparing inches to feet will give a meaningless ratio.
FAQ
What is the greatest common divisor?
It is the largest whole number that divides both values exactly. Dividing both sides of a ratio by it produces the simplest equivalent ratio.
How do I turn a ratio into a percentage?
Add the two parts to get the whole, then divide each part by that total and multiply by 100. For 3 : 1, the parts are 75% and 25%.
Can a ratio have decimals?
Yes, but it is clearer to scale both sides up until they are whole numbers. This tool rounds inputs to whole numbers before simplifying.
Related calculators
Percentage Calculator · Percent Change Calculator · Average (Mean) Calculator · Exponent Calculator · Square Root Calculator