Open Rate

Definition

Open rate is the percentage of email recipients who opened an email campaign. Formula: Open Rate = (Unique Opens ÷ Emails Delivered) × 100. A 25% open rate means 25 out of every 100 delivered emails were opened. Opens are tracked via a tiny invisible image (tracking pixel) loaded when the email is opened—if images are blocked or not loaded, opens aren't counted, making this metric imperfect. With Apple's Mail Privacy Protection (2021+), open rates have become less reliable as Apple pre-loads images for all emails, inflating open rates. Average open rates vary by industry: B2B 21.5%, retail 18.5%, non-profit 25.5%. Factors affecting open rate: subject line quality, sender name recognition, send time, list quality/engagement, mobile optimization, and inbox placement (Gmail's Promotions tab reduces opens ~50%). While less reliable than before, open rates remain useful for: comparing performance of subject lines, identifying engaged vs. disengaged subscribers, and timing send optimizations.