Sample Size Calculator

Use this free calculator to work out how many participants or responses you need for your survey or study, based on how confident you want to be in the result and how much error you are willing to accept.

How to use it

Choose your confidence level (95% is standard), set the margin of error you can live with, and leave the expected proportion at 50% unless you have a good estimate. If you are sampling from a known, finite group, enter its size for a smaller required sample.

How to read the result

The number returned is the count of completed responses you need. Because some people start and do not finish, aim to collect a little more than this. A smaller margin of error or a higher confidence level both push the required sample up.

Frequently asked questions

What is a good sample size for a dissertation survey?

It depends on your population and how precise you need to be, not a fixed number. At 95% confidence with a ±5% margin of error, you typically need around 380 responses from a large population. Use the calculator with your own figures rather than copying a generic number.

What margin of error should I use?

±5% is the common default for student and organisational surveys. Tighten it to ±3% only if you genuinely need that precision, because it sharply increases the sample you must collect.

Does population size matter?

Only for smaller, finite populations. Once the population runs into the tens of thousands, the required sample barely changes, which is why the field can be left blank for large or unknown populations.