Aspect Ratio Calculator
Calculate width or height while keeping the aspect ratio. Find the ratio of any size, use presets like 16:9, 9:16, 4:5, 1:1, 4:3 and 21:9, and look up recommended sizes for YouTube, Instagram, TikTok and other platforms.
Common ratios
Original size
×
Aspect ratio 16:9 Decimal 1.778
New size
×
Type a width or a height — the other side follows the ratio.
New size 1280 × 720 Even numbers (for video) 1280 × 720
16:9
Recommended sizes by platform
| Platform | Use | Size (px) | Ratio | |
|---|---|---|---|---|
| YouTube | Video | 1920 × 1080 | ||
| YouTube | Shorts | 1080 × 1920 | ||
| YouTube | Thumbnail | 1280 × 720 | ||
| YouTube | Channel banner | 2560 × 1440 | ||
| Square post | 1080 × 1080 | |||
| Portrait post | 1080 × 1350 | |||
| Stories / Reels | 1080 × 1920 | |||
| Landscape post | 1080 × 566 | |||
| TikTok | Video | 1080 × 1920 | ||
| Link / shared image | 1200 × 630 | |||
| X (Twitter) | Post image | 1600 × 900 | ||
| Post image | 1200 × 627 | |||
| Standard pin | 1000 × 1500 | |||
| Twitch | Stream / video | 1920 × 1080 | ||
| — | 4K UHD | 3840 × 2160 | ||
| — | Full HD | 1920 × 1080 |
Platform recommendations change from time to time — check each platform’s help pages for the latest.
How it works
- Pick a preset ratio or type your own (for example 1920 × 1080).
- Type a new width or height — the other side is calculated automatically.
- Check the platform list for recommended sizes and click one to load it.
FAQ
How do I calculate an aspect ratio?
Divide width and height by their greatest common divisor. 1920 × 1080 → both divide by 120 → 16:9. New height = new width × (ratio height ÷ ratio width).
What ratio are YouTube Shorts, Reels and TikTok?
All vertical 9:16, usually 1080 × 1920 pixels.
Why do I get decimals?
Some sizes can’t keep the exact ratio in whole pixels. The result is rounded; video encoders often prefer even numbers, which the tool also shows.