Aspect Ratio Calculator
Calculate width or height for any aspect ratio — 16:9, 4:3, 21:9, and more. Lock a ratio and scale dimensions without distortion. All client-side.
Runs in your browser — nothing uploaded
Presets:
Ratio
:
Dimensions
Edit the ratio, width, or height — the other dimension recalculates to keep the proportions exact.
Resize anything without distorting it. Set an aspect ratio — 16:9, 4:3, 21:9, or your own — then enter a width or a height and get the matching dimension instantly. Perfect for video frames, images, screens, and responsive layouts.
Private by design — your data never leaves your device
How to use it
No account, no upload — it all happens on your device.
1
Choose a preset ratio or type your own (width and height).
2
Enter a known width or height in pixels.
3
The other dimension fills in automatically to match the ratio.
4
Tweak any field — the rest stays proportional.
Common aspect ratios
Where each shape shows up.
| Ratio | Used for |
|---|---|
| 16:9 | YouTube, HD/4K video, most monitors and phones |
| 9:16 | Vertical video — Reels, TikTok, Stories |
| 4:3 | Classic monitors, some cameras, presentations |
| 1:1 | Square social posts and avatars |
| 21:9 | Ultrawide monitors and cinematic video |
Tips
- Match the source.Exporting at the wrong ratio adds letterboxing (bars) or crops your content — pick the ratio of the platform you're posting to.
- Scale, don't stretch. Keep the ratio fixed when resizing so circles stay round and faces stay natural.
- Round to whole pixels. Displays render whole pixels, so round the result if you need an exact integer size.
Frequently asked
How does the calculator keep proportions?
It holds the aspect ratio fixed. When you change the width, it recomputes the height as width × ratioHeight ÷ ratioWidth (and vice versa), so the result is always proportional — no stretching or squashing.
What's the difference between 16:9 and 4:3?
They describe the shape of a rectangle: width to height. 16:9 is widescreen (modern TVs, YouTube, most phones in landscape); 4:3 is the older, squarer format used by classic monitors and some cameras.
Is anything sent to a server?
No. The math runs entirely in your browser. Nothing you enter leaves your device.