Social media image sizes
Every platform resizes and re-compresses what you upload. Giving each one a file that already matches its dimensions is the whole trick to keeping your images sharp.
The sizes
Instagram — square post 1080 × 1080, portrait 1080 × 1350, landscape 1080 × 566, story and reel 1080 × 1920. Portrait 4:5 occupies the most feed space.
LinkedIn — post and link share 1200 × 627, square 1200 × 1200, cover banner 1584 × 396, profile photo 400 × 400 minimum, company logo 300 × 300.
Facebook — feed post 1200 × 630, story 1080 × 1920, cover photo 851 × 315, profile 320 × 320.
X — in-stream image 1600 × 900 (16:9), header 1500 × 500.
Pinterest — 1000 × 1500 (2:3). Pinterest is the one platform where tall genuinely outperforms.
YouTube — thumbnail 1280 × 720, channel art 2560 × 1440 with the safe area in the middle 1546 × 423.
Why the right size keeps things sharp
Upload a 12-megapixel photo to Instagram and it has to reduce it to 1080 pixels wide and compress it for delivery. That happens on their servers with their settings, tuned for storage cost rather than for your photograph.
Hand over a file already at the target dimensions and reasonably compressed, and their encoder has very little left to do — so it does less, and what people see stays closer to what you exported.
This is the entire reason correct dimensions matter. It is not that the platform rejects wrong sizes; it is that wrong sizes hand the platform more work, and its work is worse than yours.
Safe areas and cropping
Two traps catch people repeatedly.
Cover banners crop differently on mobile. LinkedIn and Facebook both cut the left and right edges on phones. Keep anything important — text, faces, logos — well inside the centre.
Feed previews crop to square. A landscape image may display as a centre-cropped square in some grid views. If the composition falls apart when squared off, it will fall apart in the grid.
Link previews come from your website
When you share a URL rather than an image, the platform does not use anything you chose. It reads the og:image tag from that page.
So if your own articles preview badly, the fix is on your website, not in the post. Make sure each page has an og:image at 1200 × 630, referenced by an absolute URL — a relative path is the single most common cause of a blank preview. Platforms also cache aggressively, so use their debugging tool to force a refresh after changing it.