Aspect Ratio Calculator
Find the aspect ratio of any size and scale dimensions proportionally.
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Enter a width and height and this aspect ratio calculator reduces them to the simplest whole-number ratio, shows the same shape as a decimal, and, if you add a new width, works out the height that keeps the proportions intact. It is meant for resizing photos, video frames, thumbnails and embeds without stretching or squashing them.
How the ratio and the new height are calculated
The tool finds the greatest common divisor (GCD) of the two numbers with Euclid's algorithm and divides both by it. For 1920 × 1080 the GCD is 120, so the ratio becomes 1920 ÷ 120 : 1080 ÷ 120 = 16 : 9. The decimal line is simply width ÷ height, here 1.7778.
When you fill in New width (optional), the matching height is:
new height = new width × original height ÷ original width
= 1280 × 1080 ÷ 1920 = 720
The GCD step rounds your inputs to whole numbers first, so enter pixel dimensions rather than values like 16.5.
Common ratios and where they are used
| Ratio | Typical use | Example size |
|---|---|---|
| 16 : 9 | YouTube, TVs, laptop screens | 1920 × 1080 |
| 9 : 16 | Reels, Shorts, Stories | 1080 × 1920 |
| 4 : 5 | Instagram portrait post | 1080 × 1350 |
| 1 : 1 | Square posts, profile photos | 1080 × 1080 |
| 3 : 2 | DSLR and mirrorless photos | 6000 × 4000 |
| 4 : 3 | Default on most phone cameras | 4000 × 3000 |
Why some "16:9" screens show an odd ratio
Type 1366 × 768, a very common budget-laptop resolution, and the answer is 683 : 384, not 16 : 9. A true 16 : 9 panel that is 768 pixels tall would be 1365.33 pixels wide, which is impossible, so manufacturers rounded to 1366 and kept the marketing label. Likewise 2560 × 1080 "21:9" ultrawide monitors reduce to 64 : 27. When the reduced ratio looks strange, compare the decimal instead: 1.7778 is exact 16 : 9, and 1366 × 768 gives 1.7786, close enough that nobody notices.
Worked example and practical tips
A camera photo of 6000 × 4000 needs to be 1500 pixels wide for a blog. Entering 6000, 4000 and 1500 returns 3 : 2, decimal 1.5, and a height of 1000. A few things to keep in mind:
- Scaling keeps the shape; it cannot turn a 3 : 2 photo into a 1 : 1 post. That needs cropping, which the image cropper does, while the image resizer changes the actual file's pixel size.
- Round the height to a whole pixel. For MP4 video, H.264 encoders using the usual 4:2:0 colour format need even widths and heights, so round to the nearest even number.
- In CSS you can use the ratio directly:
aspect-ratio: 16 / 9;keeps a video embed or card in shape at any screen width. - Need a width for a given height? Put the original height in the Width box, the original width in the Height box, and your target height in New width. The result is the matching width.