What an aspect ratio is
An aspect ratio is the relationship between the width and height of a picture, written as two numbers such as 16:9. It describes shape, not size. A 16:9 frame can be 1280 by 720 pixels or 3840 by 2160 pixels and still have the same proportions. Dividing width by height gives a single number: 16 divided by 9 is about 1.78, which is why 16:9 is also written as 1.78:1.
How screen shapes developed
Early cinema settled on a frame close to 4:3, often described as 1.33:1, and a slightly wider version known as the Academy ratio, around 1.37:1. Early television took the 4:3 shape as well, so films and broadcasts were broadly compatible.
When cinemas wanted to set themselves apart from television, wider formats followed. Common widescreen cinema shapes include roughly 1.85:1 and about 2.39:1. Films shot this way did not fit a 4:3 television, which led to the familiar choices of cropping the sides or adding black bars above and below the picture.
High-definition television settled on 16:9. It is often described as a compromise: it is wider than 4:3, yet not as extreme as the widest cinema formats, so both older and newer material can be shown with moderate bars. Computer monitors and online video players largely followed, and 16:9 became the default for most video on a computer or a connected TV.
Phones then changed the picture again. People naturally hold a phone upright, and apps built around that habit use tall frames, with 9:16 as the usual shape for full-screen vertical video. Square 1:1 and 4:5 portrait frames also became common in social feeds, because they take up more of a scrolling screen than a wide frame does. For how to shoot for this shape, the guide to vertical framing is the place to look.
Common ratios at a glance
| Ratio | Approx. decimal | Typical use |
|---|---|---|
| 4:3 | 1.33 | Older television, some archive footage |
| 16:9 | 1.78 | HD and UHD television, most online video |
| 1.85:1 | 1.85 | Widescreen cinema |
| 2.39:1 | 2.39 | Wide cinema formats |
| 1:1 | 1.00 | Square posts in some feeds |
| 4:5 | 0.80 | Portrait posts in some feeds |
| 9:16 | 0.56 | Full-screen vertical video on phones |
Letterbox, pillarbox and cropping
When a picture does not match the screen, a player has three basic options. It can add bars: letterboxing puts bars above and below a wide picture, and pillarboxing puts them at the sides of a narrow one. It can crop the picture to fill the screen, which loses some of the image. Or it can stretch the picture, which distorts everything and is almost always a mistake.
Bars are not a fault in the video. They preserve the full image, and many viewers prefer that to losing part of the frame.
Handling several ratios in one project
Many projects now need more than one shape: a widescreen version for a website or TV, a vertical version for short-form clips, and perhaps a square version for a feed. There are two broad approaches.
Reframing. Edit in the main shape, then make a copy of the project for each additional ratio and move the picture within the new frame so the subject stays visible. Many editing programs have a reframe or auto-crop feature, though results usually need a manual check.
Shooting with all shapes in mind. Record at a high resolution and keep important content near the centre of the frame, in a region that survives every crop. This is often called a safe area.
The arithmetic of cropping
Working through an example makes the trade-off clear. Take a 1920 by 1080 frame, which is 16:9. To crop it to 9:16 at full height, the new width is 1080 multiplied by 9 and divided by 16, which is 607.5, so about 608 pixels. That is only around 32 percent of the original width (608 divided by 1920 is about 0.317). Most of the frame is discarded, and the vertical version would be only 608 by 1080 pixels unless it is scaled up, which softens the image.
A square crop is less drastic. Keeping the full 1080 height gives a 1080 by 1080 frame, which keeps 1080 divided by 1920, or 56.25 percent, of the width.
This is why shooting wider than you need, or at a higher resolution such as 4K, gives more room for reframing. A 3840 by 2160 frame cropped to 9:16 at full height is 1215 by 2160 pixels (2160 times 9 divided by 16 equals 1215), which still exceeds 1080 pixels wide. See the article on video resolution for more on what pixel counts mean.
Practical tips
- Decide early which ratios you need, and which one is the main version.
- Use shot composition that leaves breathing room around the subject, so crops do not clip faces or key objects.
- Place titles and captions inside a safe area, away from the edges, since apps often overlay their own buttons and text on vertical video.
- Preview each version on the device it is meant for, not just on the editing monitor.
- Check export settings for each version separately, since platforms may expect different dimensions.
A single video can serve several screens, but each ratio is a different composition, and the best results usually come from treating each one deliberately.