Video aspect ratio calculator
Short answer: the missing side is width × H ÷ W (or height × W ÷ H). So 9:16 at 1080 px wide is 1920 px tall, 1:1 is 1080 × 1080, 4:5 is 1080 × 1350 and 16:9 is 1920 × 1080. Round to an even number for video. Use the calculator below for any other size.
1. Find the missing width or height
9:16 at 1,080 px wide is 1,920 px tall. Use 1,080 × 1,920 (rounded to an even number for video).
2. What ratio is this resolution?
Simplest ratio 64:27 (2.3704). Nearest common ratio: 21:9 (1.6% off).
3. Crop or bars: what a reframe costs
Fill (crop): keeps a 608 × 1,080 px slice of the source, 31.6% of its width; 656 px is cut from each side.
Fit (bars): on a 1,080 × 1,920 frame the video is 1,080 × 608 px with 656 px bars top and bottom; the video fills 31.6% of the frame.
Fill keeps the frame full but loses the edges. Fit keeps the whole picture but most of a vertical frame becomes bars. For talking-head clips, Fill with the subject centred usually works; for wide shots, read landscape to vertical.
Common video resolutions by aspect ratio
| Ratio | Shape | 720p class | 1080p class | 4K class |
|---|---|---|---|---|
| 9:16 | Vertical | 720 × 1280 | 1080 × 1920 | 2160 × 3840 |
| 1:1 | Square | 720 × 720 | 1080 × 1080 | 2160 × 2160 |
| 4:5 | Portrait | 720 × 900 | 1080 × 1350 | 2160 × 2700 |
| 16:9 | Landscape | 1280 × 720 | 1920 × 1080 | 3840 × 2160 |
| 4:3 | Classic TV | 960 × 720 | 1440 × 1080 | 2880 × 2160 |
Each row is the same shape at three sizes: the short side is 720, 1080 or 2160 px and the long side follows from the ratio.
Which ratio for which platform
| Where | Ratio | Size | Details and sources |
|---|---|---|---|
| TikTok | 9:16 | 1080 × 1920 | TikTok, Reels and Shorts sizes |
| Instagram Reels | 9:16 | 1080 × 1920 | Instagram Reels size |
| YouTube Shorts | 9:16 (square also counts) | 1080 × 1920 | YouTube Shorts size |
| Square feeds | 1:1 | 1080 × 1080 | Crop video to square |
| Standard YouTube, websites | 16:9 | 1920 × 1080 | Video sizes guide |
How to use it
- Pick a ratio. Tap a preset or type your own, such as 2.39:1 or 3:2.
- Enter the side you know. Choose width or height and type the pixels. The other side appears at once, exact and rounded to an even number.
- Check an existing file. Type its width and height in section 2 to see its simplest ratio and the nearest common one.
- Plan the reframe. In section 3, see how much of a landscape clip survives in a vertical or square frame before you edit.
- Make the clip. Open Millwards Studio to trim and export it.
Then trim and export the clip
Millwards Studio is a browser video clipper for your own videos: upload a file, trim the hook, choose 9:16, 1:1 or 16:9, add captions and export. Free exports are 720p WebM made in your browser with a watermark; Pro (£12 per month) gives 1080p MP4 with no watermark. The editor's layouts are 9:16, 1:1 and 16:9; 4:5 is in the calculator for planning only.
FAQ
What resolution is 9:16?
Common 9:16 resolutions are 720 x 1280, 1080 x 1920 and 2160 x 3840 pixels. For any width, the height is width x 16 / 9; for any height, the width is height x 9 / 16.
How do I calculate an aspect ratio from a resolution?
Divide the width and the height by their greatest common divisor. 1920 x 1080 divides by 120 to give 16:9; 1080 x 1350 divides by 270 to give 4:5.
What happens to a 16:9 video in a 9:16 frame?
If you fill the frame, you keep a slice 9/16 x 9/16 of the original width, about 31.6%, and crop the rest. If you fit the whole picture, it fills about 31.6% of the frame height and the rest is bars: on a 1080 x 1920 frame the video is 1080 x 607.5 px with about 656 px of bars above and below.
Why round video dimensions to an even number?
The common H.264 and HEVC encoders store colour at half resolution (4:2:0), so they need even widths and heights. The calculator gives the exact value and the nearest even one.
Is anything uploaded?
No. The calculator only does arithmetic in your browser. No file is needed and nothing is sent to Millwards Studio.