Sample Size Calculator
Calculate the sample size needed for a survey from the desired margin of error, expected proportion, and confidence z-score.
Formula: n = z² × p(1 − p) / e²
About Sample Size Calculator
Sample Size Calculator is a free online calculator that gives you an instant, accurate result as you type. Calculate the sample size needed for a survey from the desired margin of error, expected proportion, and confidence z-score.
The calculation uses the standard formula n = z² × p(1 − p) / e² and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
Using a proportion of 0.5 gives the most conservative (largest) sample size, which is why it is the standard default.
Frequently Asked Questions
Is Sample Size Calculator free to use?
Yes. Sample Size Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (n = z² × p(1 − p) / e²) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
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