Aspect Ratio Calculator
Calculate and convert image aspect ratios
100% free. Runs entirely in your browser - your files and data never leave your device and nothing is uploaded to any server.
Original Dimensions
Scale to New Size
Common Ratios
Matches These Common Ratios
About this tool
This calculator helps you work out an image's aspect ratio (like 16:9 or 4:3), or figure out what dimensions to use to match a target ratio - useful when you need to resize an image to fit a specific ratio without distorting it, or just want to know what ratio a set of dimensions represents.
How to use this tool
- Enter your current dimensionsType the width and height you have now, in pixels. The ratio is worked out and simplified as you type.
- Pick a target ratio, or set your ownChoose one of the presets - 1:1, 4:3, 16:9, 3:2, 2:3, 9:16, 21:9, 5:4 or 1.91:1 - or type any custom ratio you need.
- Change one side and read the otherEdit either the width or the height and the opposite value updates to keep the ratio exact, so nothing stretches.
- Use the numbers to resizeCopy the calculated dimensions into your editor, or into the Image Resizer on this site, to apply them.
How to work out a missing dimension
Divide one side by its ratio number and multiply by the other. For a 16:9 image 1920 pixels wide, the height is 1920 / 16 x 9 = 1080. For a 4:5 Instagram portrait 1080 pixels wide, the height is 1080 / 4 x 5 = 1350.
Common ratios: 16:9 for YouTube and widescreen video, 9:16 for Stories, Reels and TikTok, 1:1 for square posts, 4:5 for Instagram portraits and 3:2 or 4:3 for photo prints.
Key features
- Keeps images sharp: resizing to a matching ratio avoids the squashed or stretched look you get from forcing the wrong dimensions.
- Removes the guesswork of dividing width by height and simplifying the fraction by hand.
- Covers the ratios that platforms actually require, including 9:16 for vertical video and 1.91:1 for link previews.
- Runs entirely in your browser with no upload, so you can use it on unreleased work.
Common uses
- Video editors checking footage is 16:9 or 21:9 before an export.
- Social media managers sizing posts for a 1:1 feed image, a 9:16 story, or a 1.91:1 link card.
- Web designers working out responsive image boxes that hold their shape across breakpoints.
- Photographers converting between 3:2 camera output and 5:4 or 4:3 print sizes.
- Students and teachers fitting images into slides without distortion.
Tips for better results
- Ratios are about shape, not size: 1920x1080 and 1280x720 are both 16:9.
- Round to whole pixels at the end. A calculated 1280.5 should become 1280 or 1281, and a half pixel can produce a soft edge.
- Scaling down keeps quality; scaling far above the original will look soft no matter how exact the ratio is.
- If a target ratio does not divide cleanly, crop to the ratio instead of stretching to it.
Mistakes to avoid
- Typing a new width and height independently. Change one and let the other be calculated, or the ratio drifts.
- Confusing 16:9 with 9:16. The first is landscape, the second is vertical, and using the wrong one puts bars down the sides.
- Treating aspect ratio as resolution. A 16:9 image can be 640x360 or 3840x2160, and only the second is 4K.
- Enlarging a small image to hit a required size. Match the ratio, then start from the highest-resolution original you have.
Frequently asked questions
Enter your current dimensions or target ratio, and the calculator works out matching width/height values so you can resize proportionally without stretching the image.
16:9 (widescreen video/YouTube thumbnails), 1:1 (square, social media profile posts), 4:3 (traditional photo/screen), and 9:16 (vertical/story format) are among the most common.
This is a calculator for working out the right dimensions - use the Image Resizer or Crop tool afterward to actually apply those dimensions to your image.
Divide the known side by its ratio part and multiply by the other: for 16:9 at 1920 px wide, the height is 1920 / 16 x 9 = 1080. Enter one side and the ratio and the calculator does it for you.
1:1 for square posts, 4:5 for the tallest standard Instagram feed post, 9:16 for Stories, Reels, TikTok and Shorts, and 16:9 for YouTube videos and thumbnails.
No. 16:10 (for example 1920 x 1200) is slightly taller and common on laptops; 16:9 (1920 x 1080) is the TV and video standard. A 16:9 video on a 16:10 screen shows thin bars above and below.