Compress PNG 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. Lossless image format that supports full alpha transparency. Best for logos, graphics, and images requiring sharp edges. Use ImageSmith to compress your PNG images to the ideal file size for Substack — target under 10,000KB for optimal performance. Processing is fully browser-based — no server uploads, no privacy risk.
Recommended format
JPEG
Max file size
10,000KB
Dimensions
1200×675 for newsletter cover images
✓Email subscribers see compressed images — pre-optimize for email quality
✓Keep email-embedded images under 200KB for reliable delivery
✓Use JPEG for photographs — Substack email clients do not support WebP
✓Cover images display at 1200×675 in web and email previews