How this calculator works
A ratio is simplified by dividing both sides by their greatest common factor. 1920:1080 ÷ 120 = 16:9.
As a decimal, the ratio is A ÷ B.
To scale, the missing value is C × B ÷ A, which keeps the ratio the same.
Ratios with decimals are shown as “x : 1” instead of whole numbers.
Common ratios are worth recognising: 16:9 and 4:3 for screens, 3:2 for photos, 1:1 for squares, and mixing ratios such as 2:1 or 4:1 for paints, resins and concrete.
Worked example
A 1920 × 1080 screen
- Greatest common factor: 120.
- Simplified ratio: 16:9 (1.778 as a decimal).
- At the same ratio, a 1280-pixel-wide image is 1280 × 1080 ÷ 1920 = 720 pixels high.
Questions people ask
How do I scale a recipe with a ratio?
Divide the new number of servings by the original, then multiply each ingredient by that factor.
What is the difference between a ratio and a fraction?
A fraction compares a part with the whole; a ratio compares two parts. A 2:3 ratio means 2 parts out of 5 in total.
Can ratios have more than two parts?
Yes, for example 1:2:3 for a mix. Simplify by dividing every part by their common factor.
How do I turn a ratio into percentages?
Add the parts and divide each by the total. In 3:2, the total is 5, so the parts are 60% and 40%.
Last reviewed October 2, 2026