Aspect Ratio Calculator
Enter a width and a height to see their aspect ratio in lowest terms, such as 1920 x 1080 = 16:9, the nearest common ratio and the CSS to match. Then enter a new width or a new height and get the other side with the same ratio. A table shows the height of every common ratio at your width. Everything runs in your browser.
Resize and keep the ratio
New height: 720
Common ratios at a width of 1920
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Format ConversionAbout the Aspect Ratio Calculator
The aspect ratio of a rectangle is its width divided by its height, written as two whole numbers in lowest terms. The tool divides both sizes by their greatest common divisor, so 1920 x 1080 is exactly 16:9 and 1366 x 768 is 683:384. Because 683:384 is not a name anyone uses, the tool also tells you the closest common ratio when one is within 1%, and says how far off it is, so 1366 x 768 is about 16:9. Sizes can have decimals, and they are read exactly. To resize, it multiplies the known side by the original ratio, shows the exact value and rounds to a whole number with halves rounding up, so you can see when rounding changes the ratio slightly. The CSS output is the aspect-ratio property, and the padding-top percent is the older trick for the same box, where the height is a percent of the width. Results were compared with exact fraction arithmetic in Python on 30,000 random sizes, and the heights given by the CSS rule and the padding trick were compared with the layout of Chromium on 3,000 of them. Everything runs in your browser and nothing is uploaded.
How do you calculate an aspect ratio?▾
Divide the width and the height by their greatest common divisor. For 1920 x 1080 the greatest common divisor is 120, so the ratio is 16:9. For the decimal form, divide the width by the height: 1920 / 1080 is about 1.778.
How do I resize an image and keep the aspect ratio?▾
Multiply the new width by the original height and divide by the original width to get the new height. For a 1920 x 1080 image scaled to 1280 wide, 1280 x 1080 / 1920 is 720. Choose 'I know the new width' in the tool and it does this for you.
What is the aspect ratio of 1366 x 768?▾
It is exactly 683:384, which is about 16:9. The screen is a few pixels off true 16:9 because 768 is not divisible by 9, which is why the tool shows both the exact ratio and the closest common one.
What is the CSS aspect-ratio property?▾
It sets the ratio of a box so the browser works out the height from the width. Write aspect-ratio: 16 / 9 and a box that is 800px wide becomes 450px tall. The padding-top percent is the older way to get the same box.
Why does my resized height have a decimal?▾
Because the new size does not divide evenly. A 1000px wide 16:9 box is exactly 562.5px tall. Pixels are whole numbers, so the tool rounds to 563 and shows the exact value, and the result is off from the true ratio by a very small amount.
Is my data uploaded?▾
No. The calculation runs in your browser, and what you type is not sent anywhere or stored.