You calculate email open rate by dividing the number of opened emails by the number of delivered emails. You must multiply the result by 100 to get the percentage. For example, if 500 emails were opened out of 1,000 delivered, the open rate is 50%. You should track this metric to evaluate campaign performance. You must ensure your email service provider counts opens accurately. You can include images or tracking pixels to measure opens. You should focus on improving factors like subject lines and timing. You must regularly monitor open rates to refine your email marketing strategies.