Work out aspect ratios without the mental arithmetic
This tool takes a width and height and gives you the simplified aspect ratio, or takes a ratio and works out the dimensions to fit it. It's built for the moment you're cropping an image, sizing a video frame, or setting a grid system and need the numbers to line up exactly. Check the output against your own figures before it goes anywhere near production, since a mistyped number will produce a wrong ratio just as confidently as a right one.
Working out exact dimensions with the Aspect Ratio Calculator
The Aspect Ratio Calculator works out the missing width or height once you give it two known dimensions and the ratio you're scaling to, which saves the mental arithmetic when you're cropping a hero image or resizing a video export. This guide walks through entering your figures, locking the ratio you need, and reading the result correctly before you apply it. It only works from what you type in, so a mistyped figure will return a wrong answer without flagging it, which is worth checking before you export anything.
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Enter your known dimensions
Type in the width or height you already have, in whichever unit your layout is built on.
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Set or lock the ratio
Choose a standard ratio such as 16:9 or 4:3, or enter a custom one, and the calculator fills in the matching value automatically.
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Read the result and apply it
Check the calculated dimension against your grid or crop before exporting, since the tool works out the maths but has no way of knowing whether the result suits the composition.
Aspect Ratio Calculator
Work out the simplified ratio of any width and height, or calculate a missing dimension to match a target ratio. Ratios matter for video frames, image crops and responsive screens, keeping content proportioned correctly across devices.
Check your aspect ratio before you commit to a crop
The calculator converts between common ratios and custom dimensions, so you can confirm a canvas size, a video export, or an image crop without working the maths out by hand. It suits anyone mid-project who wants a quick answer, though it's worth checking the result against your actual output, since any calculator can misread a figure you've typed in. The site also carries a CSS unit converter and a colour contrast checker for the rest of a typical build.
No sign-up needed. Works on any device. Free to use.
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