Open Rate

Also known as: email open rate

Open rate is the percentage of delivered emails that were opened by the recipient. It is measured by embedding a 1x1 transparent tracking pixel in the email — when the recipient's client loads the pixel, the open is counted. Open rate is calculated as opens divided by delivered (not sent) emails.

Open rate has become substantially less reliable since Apple Mail Privacy Protection (2021) which pre-fetches all tracking pixels regardless of whether the user opens the email. As a result, Apple Mail opens are inflated to nearly 100%. Aggregate open rates across all clients are still directionally useful but no longer precise.

The practical use of open rate is comparing similar campaigns to each other — subject-line A vs. B to the same audience. Treating absolute open rate as a target (e.g. 'we need 80% opens') invites optimizing for the pixel rather than for actual readership.