Response rate formula
Divide the number of people who responded by the number of eligible people invited, then multiply by 100. If 250 people respond to 1,000 invitations, the response rate is 25%. Decide what counts as a response before measuring: for a survey it might be a completed questionnaire; for a media pitch it might be a direct reply. Do not mix opens or clicks into the response count.
Choose a fair denominator
When a message bounced, the recipient had no opportunity to respond. Exclude known undeliverable invitations if you can identify them reliably, and document that choice beside the result. Follow-up reminders to the same person do not add another person to the denominator. If one person replies twice, count one respondent rather than two messages.
Interpret the result carefully
A high response rate does not prove that the responses represent everyone invited. Topic, audience, timing, survey length, and the way responses are counted all matter. Compare like-for-like campaigns and consider the quality of the answers or replies alongside the percentage. Formal survey research may require a more detailed treatment of eligibility, partial interviews, and nonresponse.