Compress Images for Substack
Substack newsletter images are embedded in email and displayed on web. Images must be optimized for both email clients and web browsers, with email-safe formats prioritized. Use ImageSmith to compress your Substack images before sending — free, instant, and entirely in your browser. No account needed, no watermarks. Target under 10,000KB for best results on Substack.
Max size
10,000 KB
Format
JPEG
Size
1200×675 for newsletter cover images
- 1Email subscribers see compressed images — pre-optimize for email quality
- 2Keep email-embedded images under 200KB for reliable delivery
- 3Use JPEG for photographs — Substack email clients do not support WebP
- 4Cover images display at 1200×675 in web and email previews
Compress by format
Other platforms
Substack image compression FAQ
JPEG is the most reliable format for Substack newsletters as it renders correctly in all email clients including Outlook. Keep images under 200KB each for fast email loading.