Facebook Cover Photo Size — Free, Fast & Private
The Facebook cover photo has one official number and two display realities, and confusing them is why so many covers end up with heads cut off. The number Facebook publishes for the upload is 851×315 pixels, along with a genuinely useful performance tip from the platform itself: an sRGB JPG under 100 KB is the file that loads fastest. But what visitors see is not the upload canvas. On desktop, the cover renders at roughly 820×312 — nearly the full width, a hair less height. On mobile, it renders at roughly 640×360 — noticeably narrower and proportionally taller, which means the left and right edges of your 851-wide image simply do not exist for phone viewers. Same upload, two different windows onto it.
The safe zone is the real canvas
Work backwards from the two display crops and you get the only region guaranteed visible everywhere: a centre band of roughly 640×315 pixels. That is where the logo, the tagline, the faces, the phone number — anything that must be seen — has to live. The outer ~105 pixels on each side are mobile-invisible decoration; the extreme top and bottom slivers are desktop-trimmed. Treat the full 851×315 as the stage and the centre 640×315 as the spotlight: paint the whole stage so desktop viewers do not see empty wings, but put nothing essential outside the light. A quick self-test before uploading — cover the left and right sixth of your design with your hands. If the message survives, phones will get it too.
Cropping to a shape with no preset — the honest route
A cover is a 2.7:1 strip, and that is an unusual enough shape that the cropper on this page has no chip for it — the presets run from square to 16:9, and pretending otherwise would be false advertising. The workable route is the Free mode: drag a wide, short rectangle across your image, keeping it roughly two-and-three-quarter times as wide as it is tall. Precision to the pixel is not required here, and this is worth saying plainly — Facebook rescales whatever you upload to fit its frame, so a crop that lands near 2.7:1 displays essentially identically to an exact one. What the crop must get right is not arithmetic but placement: choose the strip of the photo where the subject sits centre, because of the safe-zone rules above. Then resize to 851 wide and you are within a few pixels of spec either way.
Why Facebook tells you to stay under 100 KB
Facebook's under-100-KB advice is about what happens after upload. Every cover is re-encoded by the platform, and heavy files are re-encoded hardest — upload a 5 MB masterpiece and the version the world sees has been through an aggressive compressor you do not control. Hand over a JPG already under 100 KB and the platform's encoder finds little left to squeeze, so what displays is close to what you made. At 851×315 — barely a quarter of a megapixel — 100 KB is a comfortable budget for a photograph and a lavish one for a graphic. The compress-to-100KB tool hits the target directly; if your cover is text-heavy flat design, it may land well under with no visible cost.
Common cover mistakes, diagnosed
Blurry cover: the source was smaller than 851×315 and got upscaled — never enlarge into the spec; start from a bigger original. Text clipped on phones: the text sat outside the 640-wide centre band; move it inward and re-upload. Colours look washed out: the file was saved in a wide-gamut colour profile and Facebook's sRGB conversion flattened it — export in sRGB, which is also what the platform's own guidance specifies. Cover looks different on your page versus the preview: you are seeing the desktop crop versus the mobile crop; check the page on a phone before signing off. None of these are fixed by uploading a bigger file — they are all geometry and encoding, which is exactly what this page's workflow controls.
Covers are one slot among many
The cover is Facebook's most unforgiving image slot because of the dual crop, but the platform has several others with their own numbers — 170×170 profile photos that display round, 1200×630 link previews, 1080×1920 Stories. The resize-for-Facebook page covers those placements, the compress-for-Facebook page handles the platform's re-encoding quirks in depth, and the social media image sizes reference puts every platform's numbers side by side.