Aspect Ratio Calculator
1366 × 768 is sold as 16:9 but reduces to 683:384, so the useful answer is often not the exact ratio but the nearest common one and how far off it is.
Find the missing width or height
Aspect ratio
| Long edge | Size | Whole pixels |
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Find the ratio of a size
How the aspect ratio calculator works
This aspect ratio calculator does the two sums people need most. Pick a ratio such as 16:9 and type a width or a height, and it gives you the other side in pixels, with every standard size of the same shape listed underneath. Or type any width and height, or read them from an image on your device, and it reduces them to the simplest ratio, shows it as a decimal and names the nearest common ratio with how far off it is.
How to calculate an aspect ratio
- Find the ratio of a size. Divide the width and height by their greatest common divisor. 1920 and 1080 share 120, which leaves 16 and 9, so 1920 × 1080 is 16:9.
- Find a missing height. Divide the width by the first number and multiply by the second. At 16:9, a 1280 px width gives 1280 ÷ 16 × 9 = 720 px.
- Find a missing width. Do the reverse: divide the height by the second number and multiply by the first. A 1920 px tall 9:16 frame is 1920 ÷ 16 × 9 = 1080 px wide.
When the answer is not a whole number, the calculator rounds it and tells you the exact figure, because 1000 px wide at 16:9 is really 562.5 px tall and no image can be half a pixel.
Why the nearest ratio matters more than the exact one
Many sizes that look standard do not reduce neatly. 1366 × 768 simplifies to 683:384 and 1080 × 1350 to 4:5, and a calculator that only divides by the common divisor leaves you to work out what 683:384 means. Several of the pages that rank for this search only solve one direction or only one ratio. This one works both ways for any ratio, compares the result against the common shapes, and can read the dimensions from an image file without uploading it.
For YouTube, 16:9 is the shape to aim for. YouTube's Help Center lists 16:9 upload resolutions from 1280 × 720 up to 7680 × 4320, and the player adapts to vertical and square videos instead. Once you know the size, crop an image to 16:9, resize it for every platform, check the YouTube thumbnail size guide, or make a thumbnail with Thumblore.
Last updated November 11, 2026.
Frequently asked questions
How do you calculate aspect ratio?
Divide the width and the height by their greatest common divisor. 1920 × 1080 share a divisor of 120, which leaves 16 and 9, so the aspect ratio is 16:9. Dividing width by height gives the same ratio as a decimal, 1.778:1.
What is 16:9 in pixels?
Any size where the width divided by 16 equals the height divided by 9. Common 16:9 sizes are 1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160. Type a width or height above to get the 16:9 size for any other number.
What aspect ratio is 1920 × 1080?
16:9. It is the same shape as 1280 × 720 and 3840 × 2160, just at a different size, which is why a 16:9 image scales between them without cropping or black bars.
How do I find the height for a width in 16:9?
Divide the width by 16 and multiply by 9. A 1280 px width gives 720 px and a 1000 px width gives 562.5 px, which rounds to 563. Pick 16:9 above and type the width to get it instantly.
Is my image uploaded anywhere?
No. When you read the size of an image, your browser opens the file on your device and only its width and height are used. Nothing is sent to a server, and the calculations run in the page.
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