How to use the aspect ratio calculator
- Pick what you want to find: the ratio, a new height for a new width, or a new width for a new height.
- Enter your width and height, or choose a ratio preset such as 16:9.
- For resizing, enter the new width or height in the last box.
- Read the result, plus the ratio, its decimal value and whether the shape is landscape, portrait or square.
The formulas
Ratio: divide width and height by their greatest common divisor (GCD). 1920 and 1080 share a GCD of 120, which leaves 16 and 9.
New height: new width × height ÷ width.
New width: new height × width ÷ height.
The decimal value (width ÷ height) is useful for comparing shapes: 16:9 is 1.778 and 4:3 is 1.333.
Worked example
A video is 1920 × 1080 and must be scaled to 1280 pixels wide for a website.
- The ratio is 16:9, and the decimal is 1.7778.
- New height = 1280 × 1080 ÷ 1920 = 720.
- The result is 1280 × 720, which keeps the 16:9 shape exactly.
For a phone post of 1080 wide at 4:5, the height is 1080 × 5 ÷ 4 = 1350 pixels.
Common sizes
| Ratio | Typical use | Example size |
|---|---|---|
| 16:9 | HD video, YouTube | 1920 × 1080 |
| 4:3 | Older TVs, tablets | 1024 × 768 |
| 1:1 | Square social posts | 1080 × 1080 |
| 9:16 | Stories and reels | 1080 × 1920 |
| 3:2 | Camera photos | 3000 × 2000 |
Tips
- Round sizes to whole pixels at the end, not in between, so errors do not build up.
- Changing the shape means cropping or adding bars. Stretching distorts the picture.
- Check the exact size the platform asks for before you export.
Related tools
Resize the picture itself with the image resizer, or cut it to a ratio with crop image. For physical sizes, use the length converter, and for scaling by a percent, the percentage calculator. Nothing is uploaded.