Sample Size
Calculate required sample size for surveys and studies
How to use Sample Size
- 1Enter your confidence level, margin of error, and an estimate of the population proportion.
- 2Add the population size if it is small and known.
- 3Read the required sample size to reach a reliable conclusion.
Why Sample Size Matters
n = z² · p(1−p) / e² (with finite-population correction)Sample size is how many observations you need to estimate a population value within a given margin of error at a chosen confidence level.
Too small a sample gives unreliable results; too large wastes effort. The calculator balances precision against cost.
Frequently asked questions
What confidence level should I use?
95% is the most common default in research; 99% gives more certainty but requires a larger sample.
What if I don't know the population proportion?
Use 0.5 (50%), which gives the most conservative, largest required sample size.
Does a bigger population always need a bigger sample?
No. Beyond a certain size, the required sample barely changes; only small populations need the finite correction.