OG image size: 1200 by 630

This size became the default across the web because several large platforms converged on a preview card near 1.91:1 at a width around 1200 pixels. It is a convention rather than a specification, which is why it holds across services that have never agreed on anything else, and why it can drift when one of them redesigns.

Getting the image to appear at all is a markup problem rather than a sizing one. The page nominates it with an og:image property in the document head, and the URL has to be absolute rather than relative, because the service fetching it has no page context to resolve against. A relative path is the single most common reason a preview shows no image.

Two further rules catch people. The image has to be reachable without a session, so anything behind authentication or a signed URL fails silently, and most services cache aggressively, so an updated image can keep showing the old one until the cache expires or is cleared through the platform's own tooling.

The image resizer has this exact size as its OG and link preview preset. Because the card is often rendered small in a feed, the text on it should be set far larger than looks comfortable at full size: a headline that reads at 1200 pixels wide can be illegible at the 300 pixels a mobile feed gives it.