Substack Newsletter Image Optimization: Prepare Clear Images for Email and Web Posts
When a Substack writer adds a chart, essay illustration, or post preview image, that file has to work in more than one place. It may appear in an email, a web post, a mobile reading view, a publication page, and a social preview card. Substack newsletter image optimization is the work of preparing a clear delivery copy for each role, not forcing one large image to serve every surface.
A strong newsletter image helps the reader understand the issue faster, gives the publication a consistent identity, and keeps the inbox experience calm. A weak image can crop the subject, blur small labels, make a chart unreadable on mobile, or load so slowly that the visual feels like clutter instead of support.
What Substack newsletter images must do
Substack images appear in different roles. A publication logo identifies the newsletter. A cover image shapes the publication presentation. A social or post preview image has to survive cropping in share cards and inbox-style surfaces. Post body images support the argument inside the essay, report, tutorial, or announcement.
Because the same reader may first see your post in an inbox and later open it on the web, the image must be clear at small widths. A chart that looks fine on your desktop editor can become unreadable on a phone. A dark editorial image can look weak in preview cards if the focal point is buried in the corners.
Official Substack image guidance to keep in mind
Substack's current support guidance lists minimum and recommended dimensions for several publication surfaces: logos at least 256 x 256 pixels with transparent background, email banners around 1100 x 220 pixels as a PNG, cover images at least 600 x 600 pixels, and social/post preview images at least 1200 x 630 pixels. Substack also notes that full-width images may be cropped when they exceed its maximum height ratio, so previewing the actual post remains essential.
Decision table for Substack image roles
| Image role | Recommended starting point | Best format | Main risk | Preview check |
|---|---|---|---|---|
| Publication logo | At least 256 x 256 px | PNG, often transparent | Tiny details disappear in small identity placements. | Publication header, profile, and mobile view. |
| Email banner or wordmark | Around 1100 x 220 px PNG | PNG | Text becomes thin or crowded in email. | Test email and mobile inbox reading. |
| Cover image | At least 600 x 600 px | JPG or PNG | Branding image is reused where the crop feels awkward. | Publication page and profile presentation. |
| Social/post preview image | At least 1200 x 630 px | JPG for editorial art, PNG for text-heavy graphics | Important subject is cropped at the edge. | Substack preview and social card crop. |
| Chart or screenshot in a post | Readable at mobile width | PNG | Small labels blur after resizing or compression. | Email body, web post, and phone-width view. |
Choose JPG, PNG, or GIF by the visual
JPG is practical for photo-like editorial images because it usually makes smooth photographs smaller. PNG is safer for charts, screenshots, diagrams, text-heavy graphics, and images with UI labels. GIF can explain a short motion, but newsletter creators should use it carefully because animations can become heavy or distracting inside an email or web post.
For charts and screenshots, protect the labels before chasing file size. Increase text size in the source chart, crop away unrelated margins, use strong contrast, then compress a delivery copy. If a reader has to pinch-zoom inside an email, the image is doing too much work.
Make preview images simple
A social preview image needs a clear focal point near the center. Avoid placing the only important text in a corner or along the bottom edge, because preview cards and inbox displays can crop differently. A clean editorial image, a simple chart excerpt, or a strong headline graphic usually works better than a dense full-page screenshot.
Continue the cluster path
FAQs
PNG is usually safest for charts because it preserves labels, lines, legends, and high-contrast edges better than a heavily compressed JPG.
Usually no. Those surfaces crop and display differently. Keep the source image, then export role-specific delivery copies for each placement.
The editor view does not guarantee the image will feel clear in email, mobile reading, or social preview. Previewing catches crop, scale, contrast, and readability issues before subscribers receive the post.
