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Square isn't the safe default on every platform

Most platforms train you to make everything 1:1. Pinterest cuts anything taller than 2:3, and vertical wins the most screen on several others.

Square is the habit because it's the safest single answer on Meta. Carry it everywhere and you'll waste most of the screen on half the platforms you buy.

Pinterest inverts it

Pinterest recommends 2:3, or 1000 x 1500 pixels, and warns that "Pins with an aspect ratio greater than 2:3 might get cut off in people's feeds". Taller isn't better here, it's cropped. Square is allowed and gives away the vertical space the feed is built around.

X says square and vertical take the same space

X's guidance is unusually direct: "1:1 is recommended as it will always render as square on desktop and mobile, timeline and profile. This and 9:16 (vertical) will take up the same amount of real estate, which is more than 16:9." So 16:9 is the one costing you.

TikTok is vertical or nothing

TikTok recommends 9:16 at 540 x 960 or larger. Horizontal and square are accepted, and both look like an import from somewhere else, which is the one thing the platform reliably punishes.

LinkedIn's numbers are per-format

The single image ad recommends 1.91:1 at 1200 x 628, with square and 4:5 also supported. The carousel is 1:1 at 1080 x 1080, and LinkedIn notes those images get "scaled to 312 x 312px", so anything that has to be legible needs to survive being shown at about a third of a business card.

Every ratio above is on the spec pages with its source and the date we read it.