Aspect Ratio Calculator
Keep the ratio when you resize: find the missing width or height, or get the simplified ratio (like 16:9) of any size. Free and private.
Report a problemFind a missing dimension
Get the ratio of a size
How to use
- To resize, set the ratio (for example 16 : 9), then type a width to get the matching height — or a height to get the matching width.
- To find a ratio, type a width and a height into the second box. It shows the simplified ratio and the decimal.
- Everything updates as you type, so there is nothing to submit.
FAQ
How do I keep the aspect ratio when resizing?
Multiply by the ratio. For a 16:9 frame, the height is the width × 9 ÷ 16 (so 1280 wide gives 720 high), and the width is the height × 16 ÷ 9. This tool does that both ways, which is exactly what you need when resizing an image or video without squashing it.
How is the simplified ratio worked out?
It divides both numbers by their greatest common divisor. 1920 × 1080 share a divisor of 120, so they reduce to 16:9. The tool also shows the decimal (1.78 for 16:9) which is handy when a size does not reduce to a tidy whole-number ratio.
Is anything I type sent anywhere?
No. It is plain arithmetic in your browser — nothing is uploaded or saved. It works offline and keeps your numbers private.