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Aspect ratio calculator

Reduce any width and height to its aspect ratio, name it and solve missing sides.

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Aspect ratio calculator
Paste one size per line — 1920x1080, 1024×768 or just 1920 1080 — and this calculator reduces each to its simplest aspect ratio instantly. 1920×1080 becomes 16:9, 1024×768 becomes 4:3, and when a size lands within one percent of a well-known ratio without matching it exactly, the tool says so with an approximation sign: 1366×768 is 683:384 ≈ 16:9. Width and height can be separated by x, ×, a comma or a space, and decimals are fine, so paper sizes like 8.5x11 work too.
Write a question mark for a missing side — 1280x? or ?x720 — and the ratio option fills it in. Set it to 16:9, 4:3, 21:9 or any custom width:height pair and the calculator solves the unknown dimension, rounded to whole pixels. Turn on "Show common resolutions" and every recognized ratio is followed by up to four standard resolutions of exactly that shape, from 1280×720 up to 3840×2160 for 16:9.
This answers the daily questions of anyone working with images and video: what ratio a video should be exported at, whether a photo fits a 3:2 print, which height keeps a responsive image from shifting the layout at a given width, and how a 9:16 vertical for social media relates to the source footage.
Everything runs locally in your browser — the sizes you type are never uploaded and there is nothing to wait for. Copy the results or download them as a .txt file when you are done.
FAQ
Which input formats are accepted?
One size per line, width first: 1920x1080, 1920×1080, 1920 1080 or 1920,1080 all work, and so do decimals like 8.5x11. Anything else gets a per-line note while the remaining lines are still processed.
How do I calculate a missing width or height?
Write it as a question mark: 1280x? solves the height and ?x720 solves the width, using the Ratio option. Set that option to any width:height pair — 16:9, 4:3, 2.35:1 — and the result is rounded to whole pixels.
What does the ≈ sign mean?
The exact reduced ratio is shown first; when it lands within 1% of a common name without equaling it, the name follows after ≈. 1366×768 reduces to 683:384, which is almost — but not exactly — 16:9.
Why doesn't 2560×1080 show as 21:9?
Because it is not: 2560×1080 reduces to 64:27, about 1.6% wider than a true 21:9, which is outside the 1% tolerance. "21:9" is a marketing label for that panel format; a mathematically exact 21:9 size like 2520×1080 is named as such.
Are the sizes I enter uploaded anywhere?
No. The calculator runs entirely in your browser and your input never leaves your device.