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Aspect ratio calculator

Set a ratio, type one dimension, get the other. Or type both and find out what ratio you have.

Simplified
16:9
As a decimal
1.7778
Recognised as
16:9
Megapixels
2.07

16:9 — YouTube, landscape video, most screens.

What this does

Three jobs in one page. Give it a ratio and one dimension and it returns the other, so 16:9 with a width of 2560 answers 1440. Give it a width and a height and it returns the ratio in lowest terms, so 1080×1350 comes back as 4:5. And it checks any size against the ratios the platforms actually use — 16:9 for YouTube and landscape video, 9:16 for Shorts, Reels and TikTok, 4:5 for the tallest an Instagram feed post can be, 1:1 for square, 21:9 for cinematic crops — so you can see at a glance whether a canvas is going to be letterboxed. Everything rounds to whole pixels, and it warns you when a result lands on an odd number, because most video encoders demand even dimensions.

How to calculate an aspect ratio

  1. 01

    Pick the ratio, or enter both sides

    Choose one of the common ratios or type your own. If you already have a width and a height, put them both in and the ratio is worked out for you.

  2. 02

    Enter the dimension you know

    The other one is calculated as you type. Lock either side to scale from it.

  3. 03

    Check it before you export

    Odd numbers are flagged — H.264 needs even dimensions and most encoders will refuse or silently resize otherwise.

Questions

What aspect ratio should a YouTube video be?

16:9 — 1920×1080 for 1080p, 2560×1440 for 1440p, 3840×2160 for 4K. YouTube pillarboxes anything narrower and letterboxes anything wider, so a 9:16 upload to the main feed shows with bars either side unless it is short enough to be treated as a Short.

What is the aspect ratio for Reels, TikTok and Shorts?

9:16, at 1080×1920. All three use the same shape and the same standard size. Keep anything you need read within the middle of the frame — the platforms' own buttons and captions sit over the edges.

Why does it warn me about odd numbers?

H.264 encodes in 16×16 macroblocks and chroma is subsampled two-to-one, so an odd width or height is invalid for the most common pixel format. Encoders either refuse the file or quietly round it, which shifts your framing by a pixel. Round to an even number yourself and you decide which way.

How do I convert 16:9 footage to 9:16 without cropping the subject?

You cannot keep all of it — 9:16 out of a 16:9 frame keeps about 32% of the width. Either crop to the action, or fit the whole frame in the middle of a 1080×1920 canvas and fill the space above and below with a title, a caption or a blurred copy of the footage.

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