Brand Kit for Newsletter Writers: Substack, ConvertKit, and Beehiiv Headers

Keep a square publication mark, a horizontal wordmark, and editable header artwork. Those source files can serve several newsletter platforms, but their upload slots have different dimensions.

A publication logo, an email banner, and a post thumbnail are separate placements. Export for each one instead of trying to reuse a single wide image everywhere.

Substack: separate the logo, email banner, and cover

Substack's image-dimension guidance lists these starting points:

Substack also describes a 14:10 ratio for post previews. Its listed social-source dimensions and displayed preview crop are not identical. Keep essential content near the center and check the actual thumbnail after publishing. Do not assume that the cover and email banner use the same slot.

A square mark should remain identifiable when small. The horizontal banner has more room for the publication name. Keep those exports beside the original vector file so a future layout change only requires another export.

Kit, formerly ConvertKit: size for the chosen template

Kit's email-editor guide explains image insertion and layout controls. Its migration guidance uses 600 pixels as a standard email image width.

That is a layout reference, not a requirement that every header must be 1200x600. Choose a height that suits your banner, then test it inside the actual template. A 1200px-wide source displayed at 600px is a possible 2x export; doubling it again is unnecessary unless the placement needs those pixels.

Use the editor preview and send yourself a test email. A landing-page image and an email header can have different display widths even when you insert them through the same media gallery.

beehiiv: logo and thumbnail have different shapes

beehiiv's publication-image guide recommends:

The thumbnail is not a universal email-header requirement. Check the image block in the email or website layout separately. If your logo needs a transparent background, test it against the theme so dark lettering does not disappear in a dark navigation bar.

Image weight and Gmail clipping are different problems

Compress large images so they load promptly, but do not confuse a hosted image's file size with the size of the email HTML. Mailchimp's explanation of Gmail clipping identifies a message-size threshold around 102 KB and says externally hosted images do not count toward it.

A heavy hosted header can load slowly without being the cause of clipping. For clipping, inspect the HTML, repeated formatting, and content length. Send a test to Gmail and confirm that the unsubscribe link is visible.

For image quality, use enough source pixels for the displayed width, then compress without making the lettering fuzzy. Keep essential information as email text so the message still makes sense when images are blocked.

Export and test each placement

Write down the publication name, square mark, horizontal wordmark, colors, and backgrounds. Then record the slot and required dimensions beside each export. The platform documentation linked above was checked on 11-Oct-2026; the uploader and preview remain the final check for your chosen template.

For your own site, a 1200x630 OG image is a useful separate link-preview export. Check which image your newsletter platform actually supplies when you share a post.

Keep the original SVG in the brand handoff folder. The podcast and YouTube guides cover the different crops needed when the publication expands into other formats.