Facebook Cover Photo Size: Getting 851 × 315 Under 100 KB From a Photo

Facebook's numbers, and the one that is a rule

Facebook's help page “Facebook Page profile picture and cover photo dimensions” holds the numbers. We read it on October 21, 2026, without logging in; its Computer, Android and iPad tabs carry the same text. One line there is a rule: the cover “Must be at least 400 pixels wide and 150 pixels tall.”

The size 851 × 315 comes from the next line, and it is a speed tip. The cover “Loads fastest as an sRGB JPG file that's 851 pixels wide, 315 pixels tall and less than 100 kilobytes.” For covers with a logo or text, the page adds that “you may get a better result by using a PNG file.”

A personal profile gets one number on its own help page: “Your cover image has to be at least 720 pixels wide.” An 851 × 315 file clears that as well. A group cover is another shape: its help page recommends “1,640px by 856px (or 1.91:1 ratio)”.

Two frames, and neither is 851 × 315

The same page says how the cover sits on screen. On a computer it “Left aligns with a full bleed and a 16:9 aspect ratio.” On a phone the frame is 2.4:1, and “The profile picture overlaps the cover photo by approximately 40 pixels on mobile devices.”

An 851 × 315 file is 2.7:1, wider than both frames. Taken literally, a frame that left aligns with a full bleed keeps the left edge and drops the right side. If the full 315-pixel height stays, a 16:9 frame shows the left 560 of 851 pixels, about two thirds. At 2.4:1, the left 756 stay.

On our lake cover, the 560-pixel line cut off the far tip of a lake that sat near the middle. The help also warns that “The left side of your cover photo will be partially covered by your profile picture”. So the safer spot for a face or a logo is left of center, clear of the left edge.

This is arithmetic from the help's wording, not a screenshot: we did not post a cover to a Page. Once yours is set, look at the Page on a computer and on a phone.

Why Thumbnail Maker stops at 851 × 320

YouTube Thumbnail Maker makes a custom size in one step, but its Width and Height start at 320 pixels. On October 21, 2026, we chose Custom size and typed 851 and 315. The Height field kept showing 315, while the label above the picture read 851 × 320.

Download JPG gave exactly that: 851 × 320 pixels and 127,563 bytes, from a 4032 × 3024 lake photo of 5,328,211 bytes. No message said the height had changed. The file clears the 400 × 150 minimum, but it is not the size the help names, and it is over 100 kilobytes.

A group cover suits this page, since both of its sides are above 320. Custom size 1640 × 856 gave a 1640 × 856 JPG of 538,709 bytes, about 0.7 seconds after we typed the height. With Cover, the picture always comes from the middle of the photo.

Crop to 851:315, then resize to 851 wide

In Crop Image, choose Custom under “Aspect ratio” and type 851:315 in “Custom ratio (N:M)”, which opens at 5:4. The field takes up to three digits a side, so the help's own numbers fit as they are.

The first frame sits near the top: 3226 × 1194 pixels on our lake photo, from row 302. Drag it over the part you want, or type numbers under “More settings”. We typed 0, 766, 4032 and 1492 for the full-width middle strip. To hold the ratio, the frame settled at 4031 × 1492.

In the row under Download JPG, choose Resize Image. It says “Continuing with the file from your last step” and opens on Percentage. Under “Set size by”, choose Exact pixels and type 851 in Width. With Lock aspect ratio on, the height follows the width, so the 851:315 crop comes out at 851 × 315.

Download JPG gave two 851 × 315 files. The lake weighed 148,914 bytes; an upright photo of an autumn tree, 171,321. Both are over 100 kilobytes, and Resize Image saves JPG at quality 90. On the 3024 × 4032 tree photo, the full-width strip was 3024 × 1119, under 28 percent of the height.

Each step was ready within two and a half seconds, in Chromium on a Mac.

Under 100 kilobytes, but whose kilobyte?

In the row under the resized cover, choose Compress Image. It opens on Balanced, which showed 56 kB for the lake and 64 kB for the tree. To land closer to the limit, choose To a size under Compression. Type 100 in Target size, keep KB as the Unit and press Update result.

About 1.3 seconds later, the lake cover weighed 98,404 bytes and the tree cover 100,512, both still 851 × 315. The page marked both targets “met”. It counts a kilobyte as 1,024 bytes, so its 100 KB is 102,400 bytes. It settles on the first quality that lands between 90 and 100 percent of the target.

Facebook's help does not say which kilobyte it means. Counted in thousands, the tree cover is 512 bytes over. Typing 97 instead brought the tree cover to 93,089 bytes, under 100,000 by either count. The lake cover stayed at 98,404 bytes, already inside the new range.

Color, PNG and what the cover leaves out

The help asks for sRGB, and the files from these tools carry no color profile at all. Our lake photo was tagged sRGB, and its cover kept the colors. The tree photo was tagged Display P3, a wider color space. Crop Image kept its color numbers but dropped the profile that tells apps how to read them.

Side by side with a proper sRGB conversion, the oranges in the tree cover looked flatter. Average saturation, on a scale of 0 to 1, was 0.60 in our cover against 0.71 in the conversion. If your photo app can export an sRGB copy, start from that copy.

A logo or text cover in PNG stays a PNG through Crop Image and Resize Image; the button reads Download PNG. Compress Image's To a size turns a PNG into a JPEG, even with Keep original format, so skip that step for a PNG. The help ties its 100 kilobytes to the JPG line only.

Facebook's help says “All cover photos are public”. Our lake photo carried its capture date, GPS position and camera model; none of the covers did. None of these tools sends the photo to our server.

To continue in another tool, PulsarKit may store a local copy of your input or result in this browser. It can remain after you close the tab or restart the browser. Clear PulsarKit’s site data to delete it.