The size of a featured image affects not only how it looks in the article, but how it appears as a card when the post is shared. If you are unsure, choose 1200x630 pixels and it will hold up almost everywhere. Here is the reasoning, and how to think about other images.
Why 1200x630
That ratio (about 1.91:1) is recommended or accepted by all of the major services that build link previews: Facebook, X, LinkedIn, Slack, Discord and others. Prepare one image and you do not need a separate version per service.
Facebook recommends at least 1200x630 for a high-resolution preview, and the smallest accepted image is 200x200. However, below 600x315 the preview switches from a large card to a small thumbnail. Treat that as the practical floor — an image that only ever appears as a thumbnail wastes the effort you put into it.
For a large card on X (summary_large_image), 1200x630 also works as-is.
In-article images follow different rules
A featured image and an in-article image do different jobs. An in-article image only has to fit the content width, so square or portrait shapes are fine. Insisting on landscape can actually hurt: on a phone, a wide image loses vertical size and detail becomes hard to read.
Diagrams, step-by-step figures and checklists are usually easier to read as squares or portraits. Choose by purpose rather than by habit.
Leave room if you overlay text
If you plan to place a title over the featured image, an image whose subject fills the centre leaves nowhere for the text. Choosing a composition with open space saves a lot of editing later.
Text is usually placed to one side. Picturing where the text will go while you are still choosing the asset saves you from redoing the work.
Watch the file size too
Correct dimensions do not help if the file is heavy. Slow pages lose readers, so aim to keep a featured image under 1 MB. A format with good compression, such as WebP, lets you cut the size without visibly changing the image.
About Visual Hub assets
We publish assets in two sizes: square (1024x1024) and landscape (1408x768). The landscape assets are generated with blog headers and social cards in mind, using compositions that deliberately leave space for overlaid text.
The landscape ratio is about 1.83:1, close to 1200x630 (about 1.91:1), so exporting one at 1200x630 rarely cuts anything important. Files are WebP, which keeps the size down.