A Facebook cover photo is 851×315 pixels — an unusually wide 2.7:1 strip that matches nothing else on the platform. The complication is that Facebook does not display the whole image the same way everywhere: desktop shows roughly 820×312, while mobile crops to about 640×360, cutting in from the sides. Anything important near the left or right edge disappears for mobile visitors, which is most of them.
Why 851 × 315?
851×315 is the size Facebook stores and serves from. Supplying exactly that avoids any resampling, which is where cover photos usually lose their crispness. Facebook also recommends keeping the file under 100 KB — above that it applies heavier compression of its own, and text and logos are the first things to visibly degrade. If your cover is mostly flat colour or text, a PNG under 100 KB will stay sharper than a JPEG.
What to Watch Out For
- Mobile crops the sides, not the top and bottom. Keep logos and text within the middle ~640px or they will be invisible on phones.
- On desktop, your profile picture overlaps the lower-left corner. Leave that area clear.
- Facebook compresses hard above 100 KB. For text-heavy covers use PNG and stay under the limit.
- The minimum is 400×150. Anything smaller gets upscaled by Facebook and looks blurry.
Resizing Without Uploading
The resizing happens entirely in your browser. Your image is never sent to a server, which matters more than it sounds — most online resizers upload your file to a machine you know nothing about. Here there is nowhere for it to go, so the question does not arise. It also means the tool keeps working with no connection once the page has loaded.
Dimensions verified: 2026-08-05 · source