Aspect Ratio Calculator
Enter an original size, then a new width or height - the other side fills in instantly so nothing gets stretched.
Quick presets
Original size
New size (fill in one side)
How the maths works
An aspect ratio is just width divided by height, written as a pair of whole numbers. To resize
without distortion you keep that ratio fixed: pick a scale factor and apply it to both sides.
In practice you usually know one new dimension, so the calculator works out the other from
new height = new width x (original height / original width), or the reverse if you
fill in the height instead. Type in either the new width or new height box and watch the
opposite side update; change the original size and the linked side recalculates too.
Reading the simplified ratio
Whatever original size you enter, the tool reduces it to lowest terms using the greatest common divisor, so 1920x1080 shows as 16:9 and 1280x1024 shows as 5:4. It also gives the decimal form (16:9 is about 1.778:1), which is the quickest way to compare two shapes at a glance - a bigger first number means a wider frame.
Common ratios and where they show up
| Ratio | Example size | Typical use |
|---|---|---|
| 16:9 | 1920 x 1080 | HD / 4K video, YouTube, most screens |
| 9:16 | 1080 x 1920 | Reels, Stories, TikTok, vertical video |
| 1:1 | 1080 x 1080 | Square social posts, avatars |
| 4:3 | 1024 x 768 | Older monitors, slideshows, tablets |
| 21:9 | 2560 x 1080 | Ultrawide monitors, cinematic video |
| 3:2 | 3000 x 2000 | Digital cameras, prints |
Common pitfalls
The classic mistake is nudging width and height independently until the numbers look right, which almost always leaves a slightly squashed or stretched result. Fixing the ratio first and deriving the second side avoids that entirely. Watch out too for fractional pixels: scaling 1920x1080 down to 1000 wide gives a height of 562.5, and rounding to 562 or 563 shifts the ratio by a hair. For video especially, stick to even numbers, because many codecs require dimensions divisible by two. Finally, remember that 21:9 monitors are rarely exactly 21:9 - the true ratio is often 64:27 or 43:18, so a preset gets you close but the panel spec is the final word.
Working with actual image files? The image resizer applies these dimensions to a photo, and the image converter helps when you need a different format. For the underlying fraction reduction, the fraction calculator shows the same GCD step in full.