Aspect Ratio Calculator
Enter a width and height to see the simplified aspect ratio, then type a new width or height to get the other side at the same ratio. You can also read the size from an image, which stays in your browser.
Original size or ratio
Enter pixels, such as 1920 × 1080, or a ratio, such as 2.39:1. Pasting 1920x1080 into either field fills both.
Or drop or paste an image anywhere on this page. Your browser reads only its pixel size.
Aspect ratio
16:9
Landscape · 1.78:1
Resize with the same ratio
Change the width or the height. The other side updates to keep the ratio.
Common 16:9 sizes
Select a size to use it as the new size.
Everything is calculated in your browser. Images you add are only read for their pixel size and are never uploaded.
How to calculate an aspect ratio
- Enter the width and height in pixels, or a ratio such as 2.39:1. You can also paste a size like 1920x1080 into either field, or pick a ratio such as 16:9 or 4:5 under Common ratios.
- Under Aspect ratio, you see the simplified ratio, its decimal form, and a preview of the shape. Sizes that come close to a standard ratio without matching it are marked with ≈.
- Under Resize with the same ratio, type a new width or height. The other side is calculated so the ratio stays the same.
- Select Copy size to copy the result as width x height, or pick one of the common sizes for that ratio. To start from a picture, select Use an image, or drop or paste it on the page.
What is an aspect ratio?
An aspect ratio describes how width relates to height, written as width:height. To find it, divide both sides by their greatest common divisor. 1920 × 1080 divided by 120 gives 16:9, and 1080 × 1350 divided by 270 gives 4:5.
The ratio describes shape, not size: 1280 × 720 and 3840 × 2160 are both 16:9. When you resize an image and want to keep its shape, multiply the new width by the second number of the ratio and divide by the first. For a 16:9 image that is 1280 pixels wide, that's 1280 × 9 ÷ 16 = 720.
Many real sizes only come close to a standard ratio. 1366 × 768 reduces to 683:384, which is 1.779:1 rather than exactly 16:9. Ultrawide monitors sold as 21:9 are usually 2560 × 1080 (64:27) or 3440 × 1440 (43:18). The calculator shows the exact ratio and marks the nearest standard one with ≈.
Need more than the ratio? The screenshot resolution checker shows the pixel size, DPI, and Retina scale of your screenshots, and the social image composer crops and pads images to the sizes social networks use.
Frequently asked questions
Is this aspect ratio calculator free?
Yes. There's no signup and no usage limit. Every calculation runs in your browser.
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. For 1920 × 1080, that's 120, so the ratio is 16:9. For the decimal form, divide the width by the height: 1920 ÷ 1080 ≈ 1.78, written as 1.78:1.
What is the aspect ratio of 1920x1080?
1920 × 1080 is 16:9. So are 1280 × 720 (HD), 2560 × 1440 (QHD), and 3840 × 2160 (4K UHD). 1920 × 1200 is 16:10, and the vertical 1080 × 1920 is 9:16.
How do I resize an image without changing the aspect ratio?
Enter the original size, then type the new width or height under Resize with the same ratio. The other side is calculated for you. If the exact result isn't a whole number, it's rounded to the nearest pixel, and the tool lists nearby sizes that keep the ratio exactly.
Why is 1366 × 768 only about 16:9?
Because 1366 ÷ 768 is 1.7786, slightly more than 16 ÷ 9 (1.7778). The exact ratio is 683:384. At 768 pixels high, an exact 16:9 width would be 1365.33 pixels, so no whole-pixel 16:9 size has that height.
Is 2560 × 1080 really 21:9?
Not exactly. 2560 × 1080 reduces to 64:27 (2.37:1), and 3440 × 1440 reduces to 43:18 (2.39:1). True 21:9 is 2.33:1. "21:9" is a marketing name for ultrawide screens, so the calculator shows both sizes as about 21:9.
Can I find the aspect ratio of an image?
Yes. Select Use an image, or drop or paste a PNG, JPG, WebP, or HEIC image on the page. The tool reads only its width and height in pixels, and the image isn't uploaded.
Can I use decimal ratios like 2.39:1?
Yes. Enter 2.39 as the width and 1 as the height. The calculator reduces it to 239:100, shows the decimal form, and marks it as about 21:9. When you resize, a whole-number side gives a whole-pixel result, and a decimal side, such as inches, gives a result with two decimals.
Need screenshots in a fixed aspect ratio?
Shotomatic's Custom Area capture on Mac has preset ratios such as 16:9, 1:1, and 4:3, and Lock aspect keeps the frame at that ratio while you resize it. Every shot in a series comes out the same shape.