Ratio Calculator
Simplify a ratio, or fill in the missing number in A : B = C : D.
How it works
- Enter the two parts of your ratio as A and B.
- Read the ratio in its simplest form.
- Optionally enter C to find the matching D so that A : B = C : D.
Frequently asked questions
How do I simplify a ratio?
Divide both parts by their greatest common divisor. 1920 : 1080 divided by 120 becomes 16 : 9.
How do I solve a proportion?
If A : B = C : D, then D = C × B ÷ A. For a 16 : 9 screen that is 1280 pixels wide, the height is 1280 × 9 ÷ 16 = 720.
Can I use decimals?
Yes. Decimal ratios such as 1.5 : 2.5 are scaled to whole numbers first and then simplified to 3 : 5.
What are ratios used for?
Scaling recipes, mixing concrete or paint, map scales, screen and photo aspect ratios, and splitting costs or profits between people.
Work with ratios and proportions
Ratios describe how two quantities relate — 16 : 9 screens, 2 : 1 rice-to-water, 1 : 50,000 maps. This calculator reduces any ratio to its simplest form and solves proportions to scale one side up or down.
Scaling recipes and images
To resize a 1920 × 1080 image to 1280 pixels wide without distortion, keep the 16 : 9 ratio: the height becomes 720. The same method scales a recipe from 4 servings to 6, or a model to real-life size.