Aspect Ratio Calculator
Simplify any pixel dimensions to a ratio, and work out the matching height for a new width without distorting anything.
Runs entirely in your browser — nothing is uploaded
Keeps the ratio.
Aspect ratio
16:9
1.7778
As a decimal
720 px tall
At 1280 wide
The ratios worth recognising
16:9 is every television, most monitors and YouTube. 4:3 is the old square-ish standard, still used by many projectors and older cameras. 1:1 is the square post. 9:16 is vertical video.
21:9 ultrawide monitors are usually 64:27 or 43:18 in truth — the marketing name is rounded, which is why this tool shows the ratio the numbers actually reduce to rather than the one on the box.
Why stretching is worse than cropping
Changing an image to a different ratio by scaling both sides independently distorts everything in it. Faces are the giveaway, and it is instantly visible even to people who could not say what is wrong.
Cropping loses content but keeps the geometry honest. If you have to change ratio, crop — and decide what leaves the frame deliberately rather than squashing the lot.
Rounding a scaled dimension
Pixels are whole numbers and most ratios do not divide evenly, so a scaled height frequently lands on a fraction. 1280 wide at 16:9 is 720 exactly; at 21:9 it is 548.57.
Round to the nearest whole pixel — a third of a pixel of distortion is not visible. Round to an even number if the result is going to be encoded as video, because most codecs require it.
Nothing is sent anywhere
Every figure on this page is worked out in your own browser. No request is made, nothing is stored between visits, and the page keeps working with the connection switched off.
Frequently asked questions
What height do I need for 1920 at 16:9?
1080. Divide the width by the ratio as a decimal: 16 ÷ 9 is 1.7778, and 1920 ÷ 1.7778 is 1080.
Why does my ultrawide say 64:27 and not 21:9?
Because 2560×1080 genuinely reduces to 64:27. 21:9 is a marketing round-up that never divided evenly — the real ratio is what the pixels say it is.
What ratio should a YouTube thumbnail be?
16:9, at 1280×720 or larger. Anything else gets letterboxed or cropped by the player, and you do not get to choose which.
Is anything sent anywhere?
No. This is arithmetic in your browser, with nothing transmitted.