Four fields — ratio width, ratio height, pixel width, pixel height — and filling any three gives you the fourth. Enter 16:9 and a width of 1440 to get the height; or enter 1280 by 1024 and be told it is 5:4, not 4:3, which is exactly why images look subtly stretched on those old monitors. Standard resolutions at your ratio are listed and clickable, including the ultrawides: a monitor sold as 21:9 is really 2.39:1, so matching is deliberately approximate by a documented margin, wide enough to include 3440 by 1440 and narrow enough never to confuse 4:3 with 5:4. A proportional preview shows the shape. Everything is calculated in your browser.
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Aspect ratio
Size in pixels
Common ratios
Standard resolutions at this ratio
Matching is approximate within 2.5%, on purpose. Monitors sold as 21:9 are really 2.37:1 or 2.39:1, so an exact match would list nothing for the ratio people actually ask for. The margin is comfortably narrower than the gap between 4:3 and 5:4, so those two never get confused.
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