About this tool
You know the width a layout gives you; the image has to stay in proportion; the math should not require a calculator app and a scratch pad. Aspect Ratio Calculator does the cross-multiplication for you. Pick a common preset — 16:9, 4:3, 1:1, 9:16 or 21:9 — or type any custom ratio, then enter either dimension and read off the other. Locking works both ways: give it the width to get the height, or the height to get the width, which is the version CSS questions usually arrive in. Results come back as exact values and rounded integers, because 1920 by 1080 is easy but 1187 pixels wide at 16:9 is not a whole number and you need to know how it rounds. A quick-reference table lists standard resolutions for the selected ratio, from small embeds up to 8K, which doubles as a cheat sheet when exporting video or sizing thumbnails. Handy for responsive image markup, video exports, slide decks, social crops and anything else where stretching is not an option. Free, instant and — like every tool here — computed entirely on your device, with nothing typed ever leaving the page.
How to use Aspect Ratio Calculator
- Pick a preset ratio or select Custom and enter your own width-to-height ratio.
- Type a width to get the matching height, or a height to get the matching width — the other field updates live.
- Use the rounded integer for pixel-exact work; the exact value for CSS fractions.
- Check the standard-resolutions table for common export sizes at the selected ratio.
Frequently asked questions
What is the difference between 16:9 and 16:10?
At the same width, 16:10 is about 11% taller — common on laptops, rare in video. Use the custom ratio fields (16 and 10) to compute 16:10 dimensions.
Why is my computed height not a whole number?
Most width-ratio combinations do not divide evenly. The tool shows the exact value plus the rounded integer; for video export, stick to even numbers since many codecs require them.
Can I lock the ratio while editing?
Yes — that is the default behavior. Whichever field you edit last is the input; the other dimension is derived from it at the current ratio.
Does this resize images?
No, it only computes dimensions. Pair it with the Image Resizer tool in the Media & Images category to actually produce a file at the computed size.