Use this free ratio calculator to simplify a ratio, compare two numbers, and find equivalent ratios in seconds. Enter two numbers, and the ratio calculator reduces them to their simplest form, shows the decimal and percentage forms, and gives equivalent ratios you can use in recipes, maps, mixing, and school math — no sign-up, no account, and no personal information needed. Your numbers are calculated in your browser and are not sent to us.
Contents: Formula · How to use · Examples · Tips · FAQ · Related tools
No sign-up required. This ratio calculator works in your browser, so the numbers you enter are not stored or sent to us. It works for whole numbers; for decimals, it rounds to the nearest whole number before simplifying.
Ratio Calculator Formula
A ratio compares two quantities by division. This ratio calculator finds the greatest common divisor (GCD) of the two numbers, then divides both numbers by that divisor to give the simplest whole-number ratio.
Simplified ratio = (First number ÷ GCD) : (Second number ÷ GCD)
Decimal form = First number ÷ Second number
First number as a percentage of the second = (First number ÷ Second number) × 100
For example, 8 : 12 has a GCD of 4. Dividing both numbers by 4 gives 2 : 3. The decimal form is 8 ÷ 12 = 0.667, and 8 is 66.7% of 12. Equivalent ratios are made by multiplying both sides by the same number, so 2 : 3 is the same as 4 : 6 and 6 : 9. The ratio calculator shows those equivalents so you can scale a recipe, a mixture, or a drawing without changing its proportions.
How to Use the Ratio Calculator
Type the first number into the first box and the second number into the second box, then tap Simplify Ratio. The ratio calculator shows the simplified ratio, the decimal form, the percentage, and two equivalent ratios. Keep the order of the numbers the same as the order in your question: for example, for 8 boys and 12 girls, enter 8 first and 12 second to get 2 : 3, not 3 : 2.
The ratio calculator is useful for cooking, where a recipe ratio must stay the same when you double it; for mixing paint, concrete, or cleaning solutions; for maps and scale drawings; and for comparing prices, scores, and quantities in everyday life. Because it works in your browser, it works in the United States, the United Kingdom, and Canada, with no unit conversion needed — a ratio has no units of its own, as long as both numbers use the same unit.
Ratio Calculator Examples
Example 1 — Simplify 8 : 12. The GCD of 8 and 12 is 4. 8 ÷ 4 = 2 and 12 ÷ 4 = 3, so the simplified ratio is 2 : 3. The decimal form is 0.667, and 8 is 66.7% of 12.
Example 2 — Simplify 15 : 25. The GCD of 15 and 25 is 5. 15 ÷ 5 = 3 and 25 ÷ 5 = 5, so the simplified ratio is 3 : 5. Equivalent ratios include 6 : 10 and 9 : 15.
Example 3 — A recipe ratio of 3 : 4, scaled up. If you need three times as much, multiply both sides by 3: 3 × 3 = 9 and 4 × 3 = 12, so the scaled ratio is 9 : 12, which simplifies back to 3 : 4. This ratio calculator check confirms that scaling does not change the proportion.
These ratio calculator examples show the same rule every time: divide both numbers by their greatest common divisor for the simplest form, and multiply both numbers by the same factor to scale up.
Ratio Calculator Tips
Always enter both numbers in the same unit — for example, both in grams or both in milliliters — or the ratio will be wrong. For background on ratios and proportions, see Wikipedia’s article on ratios. If your numbers are decimals, such as 1.5 : 2.5, first multiply both by 10 to get 15 : 25, then simplify to 3 : 5. If a ratio is given as a percentage, such as 40%, write it as 40 : 100 and simplify it to 2 : 5.
Ratio Calculator FAQ
What does a ratio calculator do? A ratio calculator simplifies a ratio to its lowest whole-number form, and shows its decimal, percentage, and equivalent forms.
What is the simplest form of 8 : 12? It is 2 : 3. Divide both numbers by their greatest common divisor, 4, to get 2 and 3.
How do I find a missing number in a ratio? Use equivalent ratios. If 3 : 4 equals 9 : ?, divide 9 by 3 to get the scale factor 3, then multiply 4 by 3 to get 12.
Can a ratio be a decimal or a fraction? Yes. A ratio of 1 : 2 is the same as the fraction 1/2 and the decimal 0.5. This ratio calculator shows the decimal form alongside the simplified ratio.
Does the order of the numbers matter? Yes. The ratio 2 : 3 is not the same as 3 : 2. Enter the numbers in the order given in your question.
Can the second number in a ratio be zero? No. A ratio compares by division, and division by zero is undefined, so enter a second number other than zero.
Related Tools
Try the Percentage Increase Calculator to measure a change, the Average Calculator for a mean, the Decimal to Fraction Calculator to turn a decimal into a fraction, and the Discount Calculator to find a sale price. Return to the PDGPT homepage to browse all free calculators by category.