Substack Image Size and File Size Limits, and How to Fit Them

Substack publishes minimum pixel sizes for its logo and wordmark and no file size limit on that page. beehiiv publishes a 5 MB guideline and a 1200 × 630 thumbnail. Ghost(Pro) sets an upload cap by plan. Each figure below comes from the platform’s own page.

Substack’s page gives no size for covers, email banners or post images, so check the upload screen in your own publication settings for the limit it enforces.

What is the best newsletter image size for email?

The pages above give no single width for body images, so this is a starting point, not a rule: export at about 1600 pixels on the long edge. That is enough detail for a retina phone screen, and well below a 12-megapixel camera frame. Wider than the reader’s screen buys nothing.

What is the Ghost image upload limit?

For Ghost(Pro) it depends on your plan: 5 MB on Free trial and Starter, 100 MB on Publisher, 250 MB on Business and 1 GB on Custom. Ghost’s theme documentation adds that it “automatically compresses and resizes images added to your post content”, so a smaller upload still helps your own storage and editor speed.

Keep each image as small as the picture allows. beehiiv’s ceiling is 5 MB, but its help page also says that large emails may get clipped in Gmail if the HTML goes over 102 KB, and that the editor warns you when a post becomes too large.

That 102 KB figure is about the HTML of the email, not the weight of the pictures, so a compressed photo does not by itself prevent clipping. What helps is fewer images, shorter markup and images that load fast on a phone. A 4 MB photo that only shows at 600 pixels wide is slow for subscribers and wasteful for you. Our starting targets, not platform rules: photos under 300 KB, screenshots under 150 KB, and check the output of every batch.

• Photos: JPG or WebP at quality 75, long edge 1600.
• Screenshots and charts: PNG if text must stay crisp, or compress to WebP.
• Animations: keep GIFs short; beehiiv asks for under 5 MB.
• Remove the GPS from phone photos before they leave your Mac.

For why a smaller image also loads faster, our Core Web Vitals measurements go into detail.

Use Compress, set the output format, quality and maximum dimension, then check the results. Smol sets quality and pixel size, not output bytes, so it cannot promise a file under a cap.

Compress to JPG rather than Convert, because quality applies to Compress. The target file size mode takes about 28 seconds for one 768 × 512 image and lands in a band, so use it only for the few files that miss.

For scale: on 24 small Kodak test photos at default settings, Smol made high-quality JPEGs 69.3% smaller. Those are 768 × 512 film scans, so your camera files will behave differently. See the benchmark page.

Drop the folder into Smol, set JPG at quality 75 and a maximum dimension, run it, then open the largest output. Four steps, about the same every issue.

1. 1

   Collect the issue’s images in one folder

   Smol writes a copy with a _compressed suffix beside each original and, by default, never overwrites it.

2. 2

   Drag the folder into Smol

   Photos, a PDF and a clip can go in together.

3. 3

   Set output, quality and size

   JPG, quality 75, maximum dimension 1600 for body images. Leave fit mode on fit so nothing is cropped.

4. 4

   Check the biggest file, then upload

   Sort by size. If one is still over your platform’s limit, lower quality or the pixel size and run that file again.

Phone photos often carry GPS. Smol strips it by default; see how to strip GPS from photos and open one output to confirm. For iPhone shots in HEIC, read batch converting HEIC to JPG.

The platform’s own editor, Preview and online compressors come first, and each has a cost. The table compares them fairly.

Our comparison of Mac image methods lays them out, and the sips guide covers the Terminal route. For a blog behind the newsletter, see blog image optimization or the WordPress image page.

Smol suits batches on a Mac. It is the wrong choice in these cases.

• You write on a phone or a Windows PC: Smol is macOS only.
• You need pixel-identical optimization: Smol always re-encodes, with no lossless mode. ImageOptim is the answer there.
• You need vector art such as SVG: Smol does not handle it.
• You need a few images resized in seconds: sips is faster than Smol for small jobs.
• You want it to guarantee a byte count: Smol sets quality and pixels, so always check the result.