Which ratios are standard?

16:9 for video and most screens, 4:3 for older television and many projectors, 21:9 for ultrawide cinema, 1:1 for square social posts and 9:16 for vertical video. Anything else usually produces bars on two sides.

Why does my video have black bars?

Because its ratio differs from the container's. A 4:3 video in a 16:9 frame gets bars at the sides; a 16:9 video in a 4:3 frame gets them top and bottom. The alternative is cropping, which loses content.

How do I work out the ratio of an existing image?

Enter both dimensions and the ratio is reduced to its simplest form. That is how you discover an image is 683:384 rather than the 16:9 someone claimed, which is usually why it does not quite fit.

Does the ratio determine print size?

No, only the shape. Physical size comes from pixel density: 1000 pixels is four inches at 250 dpi and ten inches at 100. Both have to be considered before sending anything to print.

Aspect Ratio Calculator

Scale width and height while the ratio holds.

Everything runs inside your browser. Your files never leave your device.

Result

The result appears here as you type.

Ask about Aspect Ratio Calculator

Questions about what this tool does, which option to pick, or what it can and cannot handle.

The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong. The tool itself is not guessing: it runs deterministic code on your device.

About the Aspect Ratio Calculator

An aspect ratio is the relationship between width and height, and keeping it constant is what stops resized images and video from looking stretched. This works out the missing dimension when you know the other one and the ratio.

The everyday use is resizing to fit a space. A 1920 by 1080 video in a 1280-pixel-wide container needs to be 720 tall; the arithmetic is easy and doing it repeatedly is not. Enter what you know, leave the unknown blank, and the ratio does the rest.

It also reduces arbitrary dimensions to their simplest ratio, which is how you find out that an image is 16:9 or that it is 683:384 and therefore not quite what someone told you it was. Those small discrepancies are usually the reason a video has thin black bars on two sides.

The common ratios are worth knowing by sight. 16:9 is standard video and nearly every screen. 4:3 is older television and the format most projectors still default to. 21:9 is ultrawide cinema. 1:1 is square, which social platforms favour because it fills a feed column efficiently. 9:16 is vertical, which is now the dominant format for short video and is 16:9 turned on its side.

For print, the ratio is only half the answer — the other half is pixel density. An image at 1000 pixels wide is four inches at 250 dots per inch and ten inches at 100. Ratio governs the shape, density governs the physical size, and print jobs go wrong when only one has been considered.

How to use it

1Enter the ratio you need, or two known dimensions to have it worked out.
2Fill in whichever of width or height you know and leave the other blank.
3Read the missing dimension.
4For print, check the pixel density as well — the ratio gives the shape, not the physical size.

Questions

Which ratios are standard?: 16:9 for video and most screens, 4:3 for older television and many projectors, 21:9 for ultrawide cinema, 1:1 for square social posts and 9:16 for vertical video. Anything else usually produces bars on two sides.
Why does my video have black bars?: Because its ratio differs from the container's. A 4:3 video in a 16:9 frame gets bars at the sides; a 16:9 video in a 4:3 frame gets them top and bottom. The alternative is cropping, which loses content.
How do I work out the ratio of an existing image?: Enter both dimensions and the ratio is reduced to its simplest form. That is how you discover an image is 683:384 rather than the 16:9 someone claimed, which is usually why it does not quite fit.
Does the ratio determine print size?: No, only the shape. Physical size comes from pixel density: 1000 pixels is four inches at 250 dpi and ten inches at 100. Both have to be considered before sending anything to print.