Glossary
What is aspect ratio?
By the KeyMo team · Updated
Aspect ratio is the proportion between a frame's width and its height, written as width:height. A 16:9 video is 16 units wide for every 9 tall, and 9:16 is the same shape stood upright. It describes shape, not size, so 1920x1080 and 1280x720 share one ratio even though one has more pixels.
Shape, not size
Divide width by height and you have the ratio as a single number. 16:9 is about 1.78, 1:1 is exactly 1, and 9:16 is about 0.56. Any two sizes with the same quotient have the same aspect ratio, which is why scaling a video up or down does not change its shape. Resolution counts pixels; aspect ratio only says how those pixels are arranged. See 1080p for the size side.
The ratios short-form video uses
| Platform | What its own page says | Source read |
|---|---|---|
| YouTube (computer) | 16:9 is standard; vertical or square videos are adapted by the player | YouTube Help |
| YouTube Shorts | Up to 3 minutes, square or vertical; no exact ratio named | YouTube Help |
| Instagram Reels | Upload anywhere from 1.91:1 to 9:16 | Instagram Help |
| Facebook Reels | Composer offers portrait 9:16, landscape 16:9 and square 1:1 | Meta Business Help |
| TikTok in-feed ads | 9:16 recommended; 16:9 and 1:1 also listed | TikTok Ads Manager |
| LinkedIn video | Accepts 1:2.4 up to 2.4:1 | LinkedIn Help |
The same frame cropped five ways
Take a podcast frame at 1920x1080 and keep its full height. Each new ratio keeps a different slice of the width.
| Ratio | Width kept | Share of the frame |
|---|---|---|
| 16:9 | 1920 px | 100% |
| 1:1 | 1080 px | 56% |
| 4:5 | 864 px | 45% |
| 9:16 | about 608 px | 32% |
So a vertical crop throws away about two thirds of a wide shot. If two people sit side by side, only one fits. That is the whole reason auto reframe exists, and why you should preview where the crop lands. The aspect ratio calculator does the arithmetic for other sizes.
Mistakes
- Stretching a wide video to fill a vertical frame. It distorts faces; crop instead.
- Padding with black bars (letterboxing or pillarboxing). YouTube advises against adding bars inside the video file.
- Judging a crop on a desktop preview rather than a phone.
Where KeyMo touches it
KeyMo outputs 9:16 only (1080x1920), never 16:9, and every clip is reframed to follow the face. Choose it when the destination is a vertical feed; use a different tool if you need a wide export. See vertical video.
Sources: YouTube Help: Recommended upload encoding settings (checked 11 October 2026); YouTube Help: Video resolution & aspect ratios (checked 11 October 2026); YouTube Help: Upload YouTube Shorts (checked 11 October 2026); Instagram Help: Reel size & aspect ratios on Instagram (checked 11 October 2026); Meta Business Help Center: How to use creative tools in Facebook Reels (checked 11 October 2026); TikTok Ads Manager: TikTok Auction In-Feed Ads (checked 11 October 2026); LinkedIn Help: Video sharing troubleshooting (checked 11 October 2026).