Aspect Ratio Calculator
Enter a width and height to get the simplified aspect ratio and its decimal value. You can also work the other way round: give the calculator a ratio and one dimension, and it fills in the other.
Aspect ratio
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Full dimensions
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Common aspect ratios
The shapes below are drawn to scale. Each one is a preset in the missing-dimension mode above.
1:1
A square. Used for profile pictures, product thumbnails and grid posts where every tile must align.
4:3
The older television and monitor shape, still used by many cameras, tablets and presentation slides.
3:2
The 35mm photography shape, inherited by most DSLR and mirrorless cameras and by standard print sizes.
16:9
The widescreen standard for video and most displays. 1280 × 720, 1920 × 1080 and 3840 × 2160 all sit here.
9:16
16:9 rotated. The full-screen vertical shape used by phone video, stories and short-form clips.
21:9
Ultrawide. Used by cinematic footage and ultrawide monitors; usually letterboxed on a 16:9 screen.
What an aspect ratio is
An aspect ratio is the proportional relationship between width and height, written as two numbers separated by a colon. It describes shape, not size: a 1280 × 720 image and a 3840 × 2160 image are both 16:9, even though one holds nine times as many pixels.
How this calculator works
- Your two values are read as numbers. Anything that is not a positive number is rejected before the calculation runs.
- If either value has decimals, both are scaled up by the same power of ten so the maths runs on whole numbers.
- The greatest common divisor of the two numbers is found using the Euclidean algorithm.
- Both sides are divided by that divisor, which gives the simplest form of the ratio.
- The decimal ratio is width divided by height, and the result is compared against a list of standard ratios to flag a match.
How a ratio is simplified
Take 1920 × 1080. The largest number that divides evenly into both is 120. Dividing gives 16 and 9, so the ratio is 16:9. Not every pair reduces neatly — 1001 × 611 simplifies only to 77:47, which is correct but not a standard ratio. When that happens, the decimal value is usually the more practical number to work with.
Where aspect ratios are used
- Image aspect ratios. Photos from most cameras are 3:2 or 4:3. Keeping the ratio fixed while resizing prevents stretched faces and squashed logos, and picking the right ratio before cropping saves reworking a gallery later.
- Video aspect ratios. 16:9 covers most horizontal video, 9:16 covers vertical, and 21:9 appears in cinematic footage. A mismatch shows up as black bars or as a crop that cuts off the edges of the frame.
- Screen aspect ratios. Monitors are typically 16:9 or 16:10, ultrawides are 21:9, and phones sit near 19.5:9. Two screens with the same diagonal measurement can be quite different shapes, which is why the ratio matters when comparing them.
- Social media aspect ratios. Square, portrait and story formats each expect a specific ratio. Designing to the ratio first, then exporting at the required pixel size, avoids the automatic crop that platforms apply to anything that does not fit.
Worked examples
Five sets of dimensions and the ratio each one reduces to. Try them in the calculator above.
| Dimensions | Aspect ratio | Decimal | Typically used for |
|---|---|---|---|
| 1920 × 1080 | 16:9 | 1.7778 | Full HD video, most monitors |
| 1280 × 720 | 16:9 | 1.7778 | HD video, embedded players |
| 1200 × 800 | 3:2 | 1.5000 | Camera photos, blog images |
| 1080 × 1080 | 1:1 | 1.0000 | Square social posts, avatars |
| 1080 × 1920 | 9:16 | 0.5625 | Vertical video, stories |
Frequently asked questions
What is an aspect ratio?
It is the relationship between the width and the height of an image, video or screen, written as width:height. A 16:9 frame is 16 units wide for every 9 units tall. The ratio describes shape only, so files of very different sizes can share the same ratio.
How is aspect ratio calculated?
Divide the width and the height by their greatest common divisor. For 1920 × 1080 that divisor is 120, which gives 16:9. The decimal ratio is simply width divided by height, so 1920 ÷ 1080 = 1.7778.
What is the 16:9 aspect ratio?
16:9 is the widescreen standard used by HD and 4K video, streaming platforms and most laptop and desktop displays. 1280 × 720, 1920 × 1080 and 3840 × 2160 are all 16:9. If you are exporting horizontal video and are unsure which ratio to use, this is the usual default.
What is a 1:1 aspect ratio?
1:1 means width and height are equal, producing a square. It is common for profile photos, square social posts and product thumbnails, because a square crops predictably in grid layouts and looks the same in any orientation.
Can I use decimal values?
Yes. Decimals are useful for print measurements and design canvases — 8.5 × 11 inches, for example, simplifies to 17:22. Both values are scaled to whole numbers internally before the ratio is reduced, so the result stays exact.
How do I find a missing width or height?
Switch to the Calculate Missing Dimension tab, set the ratio (or pick a preset), then type the dimension you already know. The other field fills in automatically. This is the quickest way to resize something without changing its proportions.
Why does my result not match a standard ratio?
Some dimensions simply do not reduce to a familiar ratio, usually because the image has already been cropped by a few pixels. The simplified result is still correct. If you need a standard ratio, use the missing-dimension mode to find the nearest set of dimensions that fits.
Is the calculator free and does it work on mobile?
Yes to both. There is no account, no usage limit and nothing to install, and the layout and numeric keypads are built for phones as well as desktops. If something does not behave as expected on your device, get in touch.