CSAT sample size calculator: how many survey responses you need

For a 95% confidence level and a margin of error of 5 points, you need about 385 responses from a large customer base. A smaller base needs fewer, because each answer covers a bigger share of it.

It is the range around your score that the true value probably sits in. An 88% score with a 5 point margin means the real figure is likely between 83% and 93%.

A 50/50 split needs the most responses, so it is the safe choice when you do not know the answer in advance. If most customers are satisfied, you could get by with slightly fewer.

Use the score as a rough signal. Compare it month to month, read the comments and avoid reacting to small changes. A wider margin is not useless, it is just less precise.

Ask right after the ticket closes, keep it to one question and make it answerable with a single click inside the email. Long surveys sent days later get far fewer answers.