How the aspect ratio is worked out
An aspect ratio is width divided by height. To simplify a size, divide both sides by their greatest common divisor. 1920 and 1080 share 120, so 1920×1080 becomes 16:9. 1080 and 1350 share 270, so 1080×1350 is 4:5.
Some sizes don’t simplify neatly. 1366×768 reduces to 683:384, which is close to 16:9 but not exact. That’s why the calculator also shows the nearest common ratio and how far off the size is.
Finding the other side
Pick a ratio and type either the width or the height:
- Height = width ÷ ratio. For 16:9 at 1280 wide, 1280 ÷ 1.778 = 720.
- Width = height × ratio. For 9:16 at 1920 tall, 1920 × 0.5625 = 1080.
The result is rounded to the nearest even number. H.264 and HEVC usually store colour at half resolution (4:2:0), so both sides must be divisible by 2. Many encoders refuse odd sizes or quietly crop a pixel. For 2.39:1 at 1920 wide the exact height is 803.3, so the calculator gives 804.
Common video sizes by platform
| Where | Ratio | Size |
|---|---|---|
| YouTube, Vimeo, most players | 16:9 | 1920×1080 (or 3840×2160 for 4K) |
| YouTube Shorts, TikTok, Instagram Reels and Stories | 9:16 | 1080×1920 |
| Instagram and Facebook feed, portrait | 4:5 | 1080×1350 |
| Instagram, Facebook and LinkedIn feed, square | 1:1 | 1080×1080 |
| Instagram feed, landscape | 1.91:1 | 1080×566 |
| LinkedIn and X (Twitter), landscape | 16:9 | 1920×1080 or 1280×720 |
| Older TVs and slides | 4:3 | 1440×1080 or 1024×768 |
| Ultrawide monitors | 21:9 (really 64:27) | 2560×1080 or 3440×1440 |
| Widescreen cinema | 2.39:1 | 1920×804 |
Platforms change their recommendations from time to time, so check their help pages before a big upload.
Screen recordings and odd ratios
Mac screens are not 16:9. A MacBook Air 13" is 2560×1664 (about 1.54:1) and a MacBook Pro 14" is 3024×1964, both close to 16:10. Uploaded to YouTube, these get thin black bars at the sides. To avoid them, record a 16:9 area of the screen, or crop when you export. For vertical clips, record or crop a 9:16 region rather than squeezing the whole screen.
Letterboxing, cropping and stretching
When a video’s ratio doesn’t match the screen, the player has three choices:
- Letterbox or pillarbox: add bars. Nothing is lost, but the picture is smaller.
- Crop: fill the screen and cut off the edges.
- Stretch: fill the screen and distort the picture. Avoid this.
Exporting at the platform’s ratio means none of these happen.
FAQ
What is the aspect ratio of 1920×1080?
16:9. Both sides divide by 120, giving 16 and 9. The same goes for 1280×720, 2560×1440 and 3840×2160.
What size is a 9:16 video?
The usual size is 1080×1920, which is what YouTube Shorts, TikTok and Instagram Reels expect. 720×1280 is the smaller option.
How do I calculate height from width and aspect ratio?
Divide the width by the ratio. For 16:9, height = width × 9 ÷ 16, so 1280 wide gives 720. Round to an even number for H.264 or HEVC.
What is the best aspect ratio for Instagram video?
For the feed, 4:5 (1080×1350) takes up the most space on a phone. For Reels and Stories, use 9:16 (1080×1920). Square 1:1 (1080×1080) also works in the feed.