Why Image Size Matters in Emails
Email is not a website. Images in emails face unique constraints that do not apply to web pages: inbox providers apply size limits, corporate mail servers often block large attachments, many users preview emails on mobile connections, and email clients themselves handle images inconsistently.
Most email marketing best practices recommend keeping your total email size under 100 KB (HTML + images combined). Individual inline images should generally be under 50 KB each, with hero banner images stretching to 100 KB maximum in some cases.
Optimal Image Dimensions for Email
Email templates are typically 600 pixels wide — this is the industry standard that works across Outlook, Gmail, Apple Mail, and mobile clients. Design images to these dimensions:
| Image Type | Recommended Width | Max File Size |
|---|---|---|
| Hero / header banner | 600 px | 80–100 KB |
| Product image (full width) | 600 px | 40–60 KB |
| Product image (2-column) | 280 px | 20–30 KB |
| Logo in header | 200–250 px | 10–20 KB |
| Small icons / badges | 50–80 px | 3–8 KB |
For retina displays, you can provide images at 2x dimensions (1200 px wide for a 600 px display) and set the HTML width attribute to 600 px. This makes images crisp on high-DPI screens without changing the displayed size.
Best Image Format for Email
Stick to formats with universal email client support:
- JPEG — Use for photographs and complex images. Best compression for photos. Quality 75–80 is ideal for email.
- PNG — Use for logos, icons, and images that need transparency or sharp text. Use PNG-8 (256 colours) instead of PNG-24 where possible for smaller files.
- GIF — The only widely supported animated format in email. Keep GIFs short (under 3 seconds) and under 500 KB.
Avoid WebP and AVIF in emails — Outlook and many other email clients do not support them. Always use JPEG or PNG for static images.
JPEG Quality Settings for Email Images
JPEG quality 75–80 is the sweet spot for email images. This produces files that are:
- Visually indistinguishable from the original at screen sizes
- Small enough to load quickly on mobile connections
- Well within inbox provider size limits
If an image still exceeds your target size after compression, reduce the pixel dimensions before compressing. A 600-wide image at quality 80 will almost always be under 80 KB.
Should You Embed Images or Link to Them?
There are two ways to include images in emails:
- Linked (hosted) — The image is hosted on a server and the email contains a URL reference. This is the standard approach for marketing emails. The email itself is tiny; images load when opened.
- Embedded (inline/base64) — The image data is encoded directly into the email. This increases total email size dramatically but ensures images display even when external content is blocked.
For marketing emails and newsletters, always use hosted images. Embedded images can trigger spam filters and bloat the email size. For transactional emails where display reliability matters (receipts, tickets), a small embedded logo may be appropriate.
Optimising Images With an Online Tool
The workflow for preparing images for email:
- Resize the image to your target width (600 px for full-width, 280 px for two-column)
- Compress using JPEG quality 75–80
- Check the file size — aim for under 80 KB per image
- Upload to your image host or email platform
- Always test the email by sending to yourself before broadcasting
Common Email Image Mistakes to Avoid
- Sending original camera JPEGs — A phone photo is typically 3–8 MB. Always resize and compress before using in email.
- Using images for text — Many email clients block images by default. If your key message or CTA is in an image, recipients who block images will miss it entirely. Use HTML text with image accents instead.
- No alt text — Always add alt text to images. When images are blocked, alt text tells recipients what they are missing.
- Non-standard widths — Images wider than 600 px will be scaled down on many clients, sometimes causing blurry rendering.
Summary
Email images should be 600 px wide, JPEG format at quality 75–80, and under 80 KB each. Hosted images (not embedded) are best for marketing emails. Always add alt text, test across clients before sending, and never use an original camera photo without first resizing and compressing it. Small, fast images improve deliverability, load time, and the overall experience for your subscribers.