Maths
Ratio Calculator
Simplify a ratio to its lowest terms, convert it to a decimal and percentages, and scale it to a new value.
Updated 27 Sep 2026
1920 : 1080 simplifies to 16 : 9 (a decimal ratio of 1.7778).
Enter two values to get the simplified ratio, the decimal equivalent and each side as a percentage of the whole. Enter a scale value to find the matching second term.
What is the Ratio Calculator?
A ratio compares two quantities. Simplifying divides both sides by their greatest common divisor, which gives the smallest whole numbers expressing the same relationship.
How to use the Ratio Calculator
- Enter the two values.
- Optionally enter a scale value to find what the second term becomes when the first is set to that number.
Formula
where GCD is the greatest common divisor of A and B
Decimal = A ÷ B
Percentage = A ÷ (A + B) × 100
Scaled = if A becomes N, then B becomes N × B ÷ A
The greatest common divisor is found with the Euclidean algorithm: repeatedly replace the larger number with the remainder of dividing it by the smaller, until one becomes zero. Decimal inputs are scaled to whole numbers first.
How the calculation works
Dividing both sides by the same number leaves the relationship unchanged, so dividing by the largest such number gives the simplest form. Scaling works the same way in reverse — multiply both sides by whatever factor takes the first term to your target.
Worked example
A screen 1920 pixels wide by 1080 tall:
- GCD of 1920 and 1080 = 120
- 1920 ÷ 120 = 16, 1080 ÷ 120 = 9
- Simplified ratio: 16 : 9
- As a decimal: 1.7778
- Width is 64% of the combined total, height 36%
Uses and benefits
- Reduce screen or image dimensions to a standard aspect ratio.
- Scale a recipe or a mix while keeping proportions exact.
- Convert a ratio into percentages for a report.
Frequently asked questions
Divide both sides by their greatest common divisor. For 1920:1080 the GCD is 120, giving 16:9. If the numbers share no common factor above 1, the ratio is already in its simplest form.
Yes. The calculator scales decimal inputs up to whole numbers before simplifying, so 2.5:1.5 correctly reduces to 5:3.