Whether you are exporting a video, sizing a thumbnail, or buying a monitor, the aspect ratio decides the shape of the frame. This reference lists every common ratio with its typical use and example resolutions, and includes a helper to compute the exact pixel dimensions for any ratio.
How it works
An aspect ratio is simply width divided by height, reduced to the smallest whole
numbers. A 1920 × 1080 frame has a ratio of 1920 / 1080 = 16/9, so it is written
16:9. The ratio fixes the shape, not the size — every 16:9 resolution from
1280 × 720 up to 3840 × 2160 has the same proportions.
To find a missing dimension while keeping the ratio, scale by the opposite side:
height = width × (ratioH / ratioW)
width = height × (ratioW / ratioH)For a 16:9 frame 2560 px wide, the height is 2560 × 9 / 16 = 1440 px. The tool
applies this for whichever dimension you supply and rounds to whole pixels.
Common ratios and their uses
| Ratio | Decimal | Typical use |
|---|---|---|
| 1:1 | 1.00 | Instagram feed posts, profile pictures |
| 4:3 | 1.33 | Classic TV, older computer monitors |
| 16:9 | 1.78 | Widescreen TV, YouTube, most monitors |
| 16:10 | 1.60 | MacBook displays, professional laptops |
| 21:9 | 2.33 | Ultrawide monitors, cinematic video |
| 2.39:1 | 2.39 | Anamorphic cinema (feature films) |
| 9:16 | 0.56 | TikTok, Instagram Reels, YouTube Shorts |
The 9:16 vertical ratio is increasingly important because short-form mobile video is now a dominant content format. If you are producing for TikTok or Reels, your master should be 1080 × 1920 — not a cropped 16:9 video, which will show black bars or require aggressive cropping to vertical that may cut out the subject.
Letterboxing, pillarboxing, and cropping
When the source and destination ratios differ, you have three choices:
- Letterboxing: add horizontal black bars (top and bottom) so the content fits within a wider frame. Preserves all content but wastes screen space.
- Pillarboxing: add vertical black bars (left and right) so wide content fits in a taller frame. Common when displaying old 4:3 content on 16:9 screens.
- Cropping: cut the edges of the content to fill the frame at the new ratio. Loses content at the edges but uses the full screen.
- Stretching: distort the image to fill the frame without cropping or bars. Almost always looks wrong and should be avoided.
For multi-platform delivery, master in the widest ratio needed and crop down: a 16:9 master can be cropped to 1:1 or 9:16 for social media by reframing the key subject in the centre of frame during filming.
Common gotchas
16:10 is not 16:9. These two ratios look almost identical at a glance, but they differ by about 11% in height. A 16:9 image on a 16:10 panel will show thin pillarboxing or slight vertical stretching. Many MacBooks use 16:10, so check your canvas size carefully before designing for a MacBook screenshot.
Pixel density is not aspect ratio. A Retina display may have 2× the pixel density of a standard display at the same physical aspect ratio. When working in design tools, use logical (point-based) dimensions, not physical pixels, to avoid oversizing assets.
Rounding to whole pixels. The dimension calculator rounds to the nearest whole pixel, which means very long ratios like 2.39:1 may not divide cleanly — always double-check that your computed height and width produce the exact ratio you need before committing to an export setting.