Aspect Ratio Calculator
Find the aspect ratio of a resolution and scale it to new dimensions.
What the Aspect Ratio Calculator does
An aspect ratio is width divided by height, reduced to its smallest whole-number form by the greatest common divisor. Scaling preserves that ratio, though the arithmetic rarely produces whole pixels — which is why encoders fuss about even dimensions.
Formula
Ratio = Width : Height, divided by their GCDDecimal ratio = Width ÷ HeightScaled height = Target width ÷ Decimal ratioScaled width = Target height × Decimal ratio
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Original width | number | Yes | Accepts 1 or more. |
| Original height | number | Yes | Accepts 1 or more. |
| Scale to | one of 3 options | Yes | — |
| Target width | number | In some modes | Accepts 1 or more. Shown Scale to is A target width. |
| Target height | number | In some modes | Accepts 1 or more. Shown Scale to is A target height. |
How to use it
- Choose Scale to.
- Enter Original width and Original height.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
A 1920 × 1080 resolution scaled to 1280 wide.
- Width
- 1920
- Height
- 1080
- Scale to width
- 1280
GCD is 120, so the ratio is 16:9 (1.7778). At 1280 wide the height is exactly 720.
Frequently asked questions
Why is 21:9 not exactly 21 divided by 9?
It is a marketing label. Real ultrawide panels are 64:27, which is 2.37:1 rather than 2.33:1.
Why do video encoders want even dimensions?
Chroma subsampling formats such as 4:2:0 halve the colour resolution in both directions, so odd dimensions cannot be divided cleanly.