Best practices for image-to-text ratio in HTML email

While Image-to-text ratio is important, there is not an exact formula that works effectively under all circumstances.  However, there are some rules of thumb that are considered best practices.

SpamAssassin recommends a minimum of 60% text and a maximum of 40% image coverage, with at least 400 characters of text. However, internal tests showed little effect on deliverability when the image ratio was greater, providing that other reputation and deliverability factors were good. 

Best practice recommendations

  • Strive for a good balance of text and images in a way that makes sense for your business.
  • Use enough text in the body of the message so subscribers get a sense of the message content whether images are on or off. Many email clients have images turned off by default, so an image heavy email with little text may not get a good subscriber response.
  • Use descriptive alternative text (alt text) with images to help subscribers get a sense of the message content with images off.
  • Favor a heavier use of images for emails targeted at a mobile viewership, since they make great tap targets. 
  • Send a test email to Inbox Preview before deploying to your subscribers to get data on spam filter performance.
  • Test different image-to-text ratios to determine what works best for your business.
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