Design dimensions
How to calculate aspect ratio
An aspect ratio compares width with height. Reduce both dimensions by the same divisor to name the shape, or use the ratio as a proportion to calculate a missing dimension.
Open the aspect ratio calculatorSimplify width and height into a ratio
Write the width first and height second, separated by a colon. A 1920 pixel wide image that is 1080 pixels high starts as 1920:1080.
Aspect ratio = width : height
Simplified ratio = width ÷ GCD : height ÷ GCD
The greatest common divisor of 1920 and 1080 is 120. Divide both values by 120 to get 16:9. Dividing only one side changes the shape, so both sides must use the same divisor.
If the dimensions share no divisor larger than 1, the ratio is already in its simplest whole-number form. A decimal ratio such as 1.5:1 can also be scaled to whole numbers: multiply both sides by 2 to get 3:2.
Calculate a missing width or height
Keep the ratio in width-to-height order. For a ratio of ratio width : ratio height:
Width = height × ratio width ÷ ratio height
Height = width × ratio height ÷ ratio width
Suppose a 16:9 video must be 720 pixels high. Its width is 720 × 16 ÷ 9 = 1280 pixels. If the width is 600 pixels, the matching height is 600 × 9 ÷ 16 = 337.5 pixels.
Layouts and image exports often require whole pixels. Rounding 337.5 to 338 is practical, but it introduces a very small change to the exact ratio. Keep the unrounded result during later calculations and round only the final dimensions.
Common aspect ratios
| Ratio | Example size | Typical shape |
|---|---|---|
| 1:1 | 1080 × 1080 | Square |
| 4:3 | 1600 × 1200 | Traditional screen or photo |
| 16:9 | 1920 × 1080 | Widescreen video |
| 3:2 | 1500 × 1000 | Common camera photo |
| 9:16 | 1080 × 1920 | Vertical video |
A ratio does not specify an absolute size. Both 1280 × 720 and 3840 × 2160 are 16:9, but they contain different numbers of pixels.
Avoid width and height mistakes
- Do not reverse the order. A portrait 9:16 frame is not the same as a landscape 16:9 frame.
- Use matching units. Compare pixels with pixels or centimetres with centimetres.
- Distinguish ratio from resolution. Ratio describes shape; resolution describes dimensions.
- Check cropping rules. Preserving a ratio may require cropping, letterboxing, or changing one dimension.
Calculate dimensions with ToolPixels
The free Aspect Ratio Calculator can simplify whole-number dimensions, find a missing width, or find a missing height. Choose the calculation, enter the ratio and known dimension, then copy the exact and nearest whole-pixel result.