Aspect Ratio Calculator

Give this calculator any two of width, height, and aspect ratio, and it hands you the third. Scaling a 1920 by 1080 video to fit a 1280 pixel column? It tells you 720. Wondering what ratio 1080 by 1350 actually is? It simplifies to 4:5 for you. Presets cover the ratios you meet daily (16:9, 4:3, 1:1, 9:16, and 21:9), and a scaling mode resizes any known dimensions to a target width or height with zero distortion.

It is all local math in your browser, nothing uploaded, no signup. I built it because I was doing this arithmetic in a phone calculator several times a week, and cross-multiplication at 11 pm is exactly how images end up subtly squashed.

How to use

1. Choose what you know: width and height, width and ratio, or height and ratio.
2. Type your two known values. The missing one appears instantly.
3. Or pick a preset like 16:9 or 9:16 and enter one dimension to get the other.
4. To scale an existing size, enter its current width and height, then the target width or height you need to hit.
5. Read the scaled dimensions, calculated to preserve the exact proportions.
6. Use the simplify feature to see any dimension pair reduced to its cleanest ratio, like 1920 by 1080 becoming 16:9.

Why use our aspect ratio calculator?

Distortion happens one lazy number at a time. Resize a 16:9 thumbnail to 400 by 250 instead of 400 by 225 and every face in it gets stretched. Nobody consciously chooses that; it happens because the correct height was not obvious in the moment. This tool makes it obvious, which is the entire job.

The ratio simplifier is the feature I did not know I needed until I had it. Handed a client asset at 1620 by 1080, you can know instantly that it is 3:2 and plan accordingly, rather than eyeballing whether it is close enough to 16:9. It also settles arguments: 1080 by 1350, the classic Instagram portrait size, is exactly 4:5, not almost 4:5.

If you build for the web, the same ratios flow straight into modern CSS, where the aspect-ratio property reserves space for media before it loads and kills layout shift. MDN's aspect-ratio documentation covers the syntax. I use this calculator to work out the ratio, then hand CSS the simplified fraction it wants.

Numbers first, pixels second. Once the calculator tells you the target size, the image resizer applies it to an actual file, and the crop image tool handles the cases where you need to change the ratio rather than preserve it. For social share images, my OG image generator already bakes in the 1200 by 630 that link previews expect, so that one common case never needs calculating at all.

There is also a quiet compounding benefit: consistency. When every thumbnail on a page shares an exact ratio, grids line up and nothing looks accidentally amateur. I standardized the screenshots on this site to a single ratio using this calculator, and the tidiness was noticeable the same day. Pick your ratios once, write them down, and let the calculator enforce them every time a new image shows up.

Who is this tool for?

Video work. Timeline exports, YouTube uploads at 16:9, Shorts and Reels at 9:16, and the eternal question of what height a 1440 wide preview should be (810, for the record). The presets cover the standard frames and the calculator covers the odd ones.

Responsive images. Designers hand off at one size and screens demand ten. Scaling a 1600 by 900 hero to a 375 pixel phone width means a 211 pixel height, and getting that number into the markup keeps the browser from reflowing the page as images arrive.

Print and slides. Fitting a 3:2 photo onto a 4:3 slide or a letter-size page means something gets letterboxed or cropped, and the calculator shows exactly how much before you commit either way.

Monitor and game setups. Ultrawide resolutions like 3440 by 1440 confuse everything. The simplifier confirms what a display really is (21.5:9, close to but not exactly 21:9), and the scaler works out what content fits it.

Frequently asked questions