Sample size calculator
Plan the minimum number of observations for a proportion or mean. Choose a confidence level and margin of error, with an optional finite population correction.
Your numbers stay in this browser. No account or upload to the server is needed.
How do I use this page?
- Choose planning for a proportion or mean and the confidence level.
- Enter the margin plus p or expected σ. For a proportion, you may also enter population N.
- Read the rounded-up result and complete formula substitution.
Method and worked example
For a proportion, n0=z²p(1−p)/E². When no prior p estimate exists, 0.5 gives the conservative largest sample.
For a mean, n=(zσ/E)². Estimate σ from a pilot or comparable previous data.
For a known finite population, the tool applies n=n0/[1+(n0−1)/N]. It always rounds up. These formulas do not include nonresponse or a complex sampling design.
Proportion example: 95% confidence, a 5 percentage-point margin and p=0.5 gives n0≈384.15, so the minimum is 385 observations.