Ratio Calculator
This ratio calculator reduces any ratio A:B to its simplest form, shows it as a decimal and tells you what share of the total each part represents. Switch to scale mode to find a missing side: the height of a 16:9 video at a given width, the oil for a fuel mix, or ingredient amounts for a bigger batch. Decimals are accepted.
Updated
Results
- Decimal value (A ÷ B)
- Share of A in the totalA ÷ (A + B)
- Share of B in the totalB ÷ (A + B)
- Missing valueShown in scale mode; same unit as the value you entered
Results are estimates. See the methodology below.
How to use the ratio calculator
- Enter A and B, the two terms of your ratio, for example 1920 and 1080 for a screen resolution. Both must be greater than zero.
- Choose a mode: Simplify reduces the ratio; Scale keeps the same proportions at a new size.
- In scale mode, pick which side you already know at the new size (A or B) and enter that value.
Simplify mode shows the reduced ratio, its decimal value (A ÷ B) and the percentage share of each part. Scale mode adds the missing value and the scaled ratio, such as 1280:720.
How ratios are simplified and scaled
Simplifying
A ratio is simplified by dividing both terms by their greatest common divisor (GCD), the largest whole number that divides both evenly. For 1920:1080 the GCD is 120, giving 16:9. If either term has decimals, the calculator first multiplies both by the same power of ten (up to six decimal places) to make them whole numbers, then divides by the GCD. That is how 1.5:2.25 becomes 150:225 and then 2:3.
Decimal value and shares
- Decimal value = A ÷ B.
- Share of A = A ÷ (A + B) × 100%, and likewise for B. The two shares always add up to 100%.
Scaling
To keep the same ratio at a new size, the calculator solves a proportion. If you know the new A, the missing B is new A × B ÷ A; if you know the new B, the missing A is new B × A ÷ B. Results can be fractional. Round them to suit your use, for example to whole pixels or to a measuring spoon you own.
Examples
1. Screen aspect ratio
A 1920 × 1080 monitor simplifies to 16:9. The decimal value is 1.777778, and the width makes up 64.00% of the sum of the two sides while the height makes up 36.00%. An ultrawide 2560 × 1080 display simplifies to 64:27 (decimal 2.37037), which is why it is marketed under the rounded label 21:9.
2. Resizing a video
You want a 16:9 video that is 1280 pixels wide. Enter A = 16, B = 9, choose scale, set the known side to A and the new value to 1280. The missing height is 720, so the scaled ratio is 1280:720. For a 4:3 image that must be 1080 pixels tall, the width comes out to 1440.
3. Two-stroke fuel mix
A chainsaw calls for a 50:1 gas-to-oil mix. For one gallon of gas (128 fl oz), enter A = 50, B = 1, scale on side A with 128: you need 2.56 fl oz of oil. Always follow your equipment manual's ratio.
4. Recipe proportions
A dressing uses 1.5 cups of vinegar to 2.25 cups of oil. The calculator simplifies this to 2:3: 40% vinegar and 60% oil, whatever the batch size.
Reading your results
The order matters: 16:9 is not the same as 9:16, which is a vertical phone video. A ratio compares two parts, while a share compares one part to the whole. In a 2:3 ratio the first part is 2 out of 5, or 40%, not 2/3 of the total. Mixing these up is a common source of errors in recipes, paint mixes and survey results.
Frequently asked questions
How do I simplify a ratio by hand?
Find the largest number that divides both terms evenly and divide each term by it. For 12:18 that number is 6, so the ratio simplifies to 2:3. If you can't spot the GCD, keep dividing by small common factors such as 2, 3 and 5 until none are left.
How do I calculate an aspect ratio from a resolution?
Enter the width as A and the height as B in simplify mode. The result is the aspect ratio: 1920 × 1080 and 1280 × 720 both give 16:9, while 1440 × 1080 gives 4:3.
Can a ratio contain decimals?
Yes. A ratio of 1.5:2.25 is valid and is equivalent to 2:3. The calculator converts decimals to whole numbers before simplifying, so the simplified form uses integers.
What is the difference between a ratio and a fraction?
A fraction compares a part to the whole, while a ratio can compare any two quantities, including part to part. In a class with 12 girls and 18 boys, the girls-to-boys ratio is 2:3, but girls make up 2/5 of the class.
Why can't I enter zero?
A ratio with a zero term can't be simplified or scaled meaningfully, and the decimal value would require dividing by zero. All values must be greater than zero.
Sources
Results are mathematical calculations based on the values you enter. For fuel mixes, chemicals or medication, always follow the manufacturer's or professional's instructions.