The Threads Post Image size (1080×1350px)
Threads, Meta's text-forward app connected to Instagram, supports images in posts, and 1080x1350 at a 4:5 portrait ratio is the tallest shape that displays fully without the feed cropping it. Because Threads shares much of Instagram's image handling, the same 4:5 that maximizes feed space on Instagram works here too, giving your photo more vertical presence as people scroll a fast-moving, conversation-driven timeline.
The advantage of 4:5 over a square is simple: a taller image takes up more of the screen, so it stops the scroll more effectively in a feed that is mostly text. At 1080 pixels wide your image matches the feed's display width, so Threads serves it with minimal recompression and fine detail stays sharp. Going taller than 4:5 risks the feed cropping your image or pushing it into an expanded view, so 1080x1350 is the practical ceiling for a clean, fully visible post.
Since Threads is built around discussion, images often support a point rather than stand alone, so make sure any text in the image is legible at feed size and keep the key subject centered where it will not be clipped by the feed's crop or an inline preview. Everything here resizes 100% in your browser with no upload and for free, so your photos stay private on your device. Threads is still evolving quickly and Meta adjusts its supported image sizes and feed behavior, so verify the current spec before an important post.