Substack Image Sizes, Formats, Preview Images, and Email Readability Explained
When a publisher prepares a Substack logo, cover image, post preview image, article header, chart, screenshot, or inline photo, the right export depends on the role. Substack image size questions are really role questions: where will the image appear, what must the reader notice first, and how small might it become in email or mobile reading?
This guide separates the decisions so you can prepare a source image once, then export a clean delivery copy for the exact Substack surface.
Official size guidance by role
Substack's current image guidance gives useful starting points: logos should be at least 256 x 256 pixels, email banners are recommended around 1100 x 220 pixels as PNG, cover images should be at least 600 x 600 pixels, and social/post preview images should be at least 1200 x 630 pixels. Substack also supports common uploaded image formats in posts, including AVIF, GIF, JPG, JPEG, PNG, and WebP.
These numbers are not a substitute for previewing. Publication settings, editor controls, email layout, mobile view, and social preview surfaces can change how the image is presented. Treat official dimensions as a starting canvas, then check the actual Substack preview before publishing.
Role-based image table
| Image role | Recommended size/ratio | Best format/export choice | Main risk | What to preview |
|---|---|---|---|---|
| Publication logo | At least 256 x 256 px | PNG, often transparent | Fine detail disappears when shown small. | Header, profile, and mobile publication identity. |
| Email banner or wordmark | Around 1100 x 220 px PNG | PNG with strong contrast | Thin text or crowded branding in email. | Test email, mobile inbox, and publication header. |
| Cover image | At least 600 x 600 px | JPG for photos, PNG for graphic covers | Inconsistent brand presentation if reused from another role. | Publication page and profile layout. |
| Social/post preview image | At least 1200 x 630 px | JPG for editorial image, PNG for text graphic | Crop hides the main subject or text. | Post settings, web preview, and share card crop. |
| Post body chart | Readable in a narrow email column | PNG | Axis labels and legends become unreadable. | Email body and phone-width reading. |
| Screenshot or UI image | Crop to the interface area that matters | PNG | UI labels blur after JPG compression. | Mobile readability and screenshot text clarity. |
| Animated explanation | Short and tightly cropped | GIF used carefully | Heavy animation distracts or slows the post. | Load feel, loop length, and whether motion is necessary. |
When JPG is practical
Use JPG for photo-like editorial images, portraits, scenes, and soft illustrations where small compression artifacts will not harm the message. JPG is not ideal for tiny text, charts, dashboards, or screenshots with UI labels because compression can create fuzz around edges.
When PNG is safer
Use PNG for charts, screenshots, diagrams, quote graphics with text, and UI images. PNG usually protects edges and labels better. If the PNG is large, crop first and then create a lighter delivery copy. Avoid shrinking it until the chart technically fits but no longer explains the data.
When GIF should be used carefully
GIF can show a short interaction, but a long animated newsletter image can feel heavy in both email and web post contexts. If motion is not essential, a still screenshot with a clear caption is often better. If motion is essential, keep the frame area small, the loop short, and the surrounding explanation clear.
Connect this decision to the full guide
FAQs
PNG is usually better for screenshots because it protects UI labels and sharp text. JPG is better for photo-like images where exact edges are less important.
Substack recommends at least 1200 x 630 pixels for social or post preview images. Keep the focal point simple and preview the crop before publishing.
Substack supports WebP uploads in posts, but JPG and PNG are still safer default delivery choices when the image may be reused across email, web, social, and external workflows.
