The near-universal size for link previews on Facebook, X, Slack, WhatsApp and most other platforms.
Target: 1200×630px
1200×630px is the size specified by the Open Graph protocol for the 'og:image' meta tag — the image that shows up when a link is shared on Facebook, X, Slack, Discord, WhatsApp, iMessage and most other platforms that generate a link preview card. It is a 1.91:1 ratio, close enough to widescreen that it displays without visible letterboxing on almost every platform's card.
Unlike a platform-specific size, this one image can be reused as the single 'og:image' for an entire website, which is exactly why it has become the de-facto default across the web rather than each platform defining its own separate standard.
Nearly — a 3px difference in height that has no visible effect. A single 1200×630 image works correctly as both a generic Open Graph image and a LinkedIn share image without needing two separate exports.
Most platforms will still display it, but they crop or letterbox to fit their card, which can cut off text or a logo positioned near the edge — exact-size images avoid that entirely.
JPG is the safest default for a photo-based share image; use PNG only if the image needs a transparent background or contains flat-colour graphics and text that must stay perfectly sharp.