Enter the size
Width and height in pixels, or any unit.
Aspect ratio calculator
Enter a width and a height to get the aspect ratio in its simplest form. Then enter a new width or height to find the other side so the proportions stay the same.
- Free
- No sign-up
- Runs in your browser
100% private — the calculation is done in your browser and nothing is sent to any server.
How it works
Read the ratio
The simplified ratio, its decimal value and the closest common one.
Resize keeping proportions
Enter a new width or height to get the matching side.
Keep the shape when you change the size
An aspect ratio describes the shape of a rectangle as the relation between its width and its height, written like 16:9. Two sizes with the same ratio have the same shape, whatever their size: a 1920 by 1080 image and a 1280 by 720 image are both 16:9. Knowing the ratio is essential when you resize an image, crop a photo for a social network, choose a video resolution, set the size of an embedded player or design a layout, because a wrong ratio means stretched, squashed or cropped content.
How the ratio is found
The width and the height are divided by their greatest common divisor, which reduces them to the smallest whole numbers with the same relation. 1920 and 1080 share a divisor of 120, giving 16 and 9. The decimal value, width divided by height, is shown too: 1.7778 for 16:9. When the ratio is not a whole-number pattern you recognise, the tool also names the closest common ratio if it is within about two percent, which helps with sizes that are rounded or cropped a little.
Resize without distorting
To scale an image, enter the width you need and the tool works out the height that keeps the same ratio, or the other way round. The result is shown with decimals and also rounded to a whole pixel, since pixel sizes must be whole numbers. Rounding may make the ratio differ very slightly, which is invisible in practice.
Common ratios and where they are used
- 16:9 for video, screens and most presentations.
- 9:16 for vertical video and stories.
- 4:3 for older screens, tablets and some photo formats.
- 1:1 for square posts and profile pictures.
- 3:2 for photographs from many cameras and 10 by 15 prints.
- 21:9 for ultrawide monitors and cinema-style video.
What it does not do
It works out proportions only. It does not resize or crop images; for that, use the image resizer, which can keep the ratio or fit an image to an exact size. Ratios involving physical print sizes also depend on resolution, which is not part of this calculation.
Frequently asked questions
How do I find the aspect ratio of an image?
Enter its width and height. The tool divides both by their greatest common divisor, so 1920 by 1080 becomes 16:9.
How do I resize an image keeping its proportions?
Enter the original size, then a new width to get the matching height, or a new height to get the matching width.
What is the aspect ratio of Full HD?
Full HD, 1920 by 1080, is 16:9, as are HD (1280 by 720) and 4K (3840 by 2160).
Why is my ratio not exactly 16:9?
The size may have been rounded or cropped. The tool shows the exact ratio and, when it is close, the nearest common one.
Can I use it for something other than pixels?
Yes. Any unit works, since only the relation between the two numbers matters.
Are my numbers sent anywhere?
No. The calculation is done in your browser.
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