Aspect ratio calculator

How to use the aspect ratio calculator

1. 01Enter the width and height of your video or image.
2. 02Read the reduced aspect ratio and its decimal value.
3. 03Pick a target ratio and enter one side to get the other, raw and rounded to an even pixel count.

Converting 16:9 to 9:16

16:9 and 9:16 are the same two numbers the other way round, but converting between them is not a case of rotating or stretching the frame: a 1920x1080 image squashed into 1080x1920 would distort everything in it. What actually changes is the crop. Going from widescreen to vertical means choosing a narrower slice of the original frame, usually built around whoever or whatever the shot is centred on, and discarding the rest.

This calculator handles the arithmetic side of that job: enter your source width and height, pick 9:16 vertical as the target ratio, and enter the side you already know to get the other side, both as an exact figure and rounded to the nearest even pixel count. What it will not do is choose the crop for you: deciding where the vertical frame sits inside the wider shot, so a speaker's face stays in frame as they move, is a judgement call, not a calculation.

A single 16:9 source can be cropped many different ways for 9:16, and the right one usually changes shot to shot: a static interview crops differently from a shot where someone walks across frame. That is a reframing decision made per clip, on top of the maths this calculator gives you.

Why video dimensions should be even numbers

Most common video codecs, including H.264, store colour information at a lower resolution than brightness information, a technique called chroma subsampling. That scheme divides the frame into 2x2 blocks of pixels, which only works cleanly if both the width and the height are even numbers: an odd dimension leaves a block with no clean pair to subsample.

In practice this means an odd width or height is either rejected by the encoder outright or silently rounded to the nearest even number before encoding, which is rarely the outcome you want if you calculated that dimension deliberately. Working in even numbers from the start avoids the surprise.

This calculator's resize row always shows two figures for the side it works out: the exact, unrounded result of the ratio maths, and the same figure rounded to the nearest even number, ready to hand to an encoder without it making that decision for you.

Common video aspect ratios

16:9 widescreen is the standard shape for a computer or television screen, and it is what YouTube treats as its default aspect ratio for a standard upload. 9:16 vertical is the mirror image of it, filling a phone screen held upright, and it is the ratio behind Reels, Shorts and most short-form vertical placements across the major platforms.

1:1 square sits exactly between the two: LinkedIn's feed, for example, still offers it as a video ad option. 4:5 portrait is a milder crop than full 9:16, and LinkedIn also lists it as a vertical option alongside 9:16: taller than square but not as tall as vertical, useful when a feed placement wants more height than 1:1 without going all the way to a phone-filling frame. 4:3 is the older, closer-to-square shape from before widescreen became standard, and still turns up in archive footage and some presentation formats.

None of these labels are the only valid choice for a given project: they are common starting points, and the calculator above works with any width and height you enter, common ratio or not.

Questions about the aspect ratio calculator

How do I calculate aspect ratio?

Divide the width and height by their greatest common divisor to write them as a simplified ratio: 1920 and 1080 share a greatest common divisor of 120, so 1920x1080 reduces to 16:9. This calculator does that step for you: enter the two numbers and it returns the reduced ratio and its decimal value directly.

What aspect ratio is 1920x1080?

16:9. Both numbers divide evenly by 120, giving 16:9, the standard widescreen ratio for a computer or television screen and YouTube's default aspect ratio for a standard upload.

What is the aspect ratio for Instagram Reels?

9:16. Meta's ads guide states 1440x2560 pixels as the resolution for the Reels ads placement, which reduces to the same 9:16 ratio as every other vertical, full-screen format.

Is 21:9 an exact ratio?

Not quite. A common 21:9 resolution, 2560x1080, actually reduces to 64:27 once you divide out the greatest common divisor, not a clean 21:9. "21:9" is a marketing approximation for a family of ultra-widescreen resolutions rather than one exact mathematical ratio.

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Updated 22 September 2026 · All free tools