Sample Size Calculator
Set the confidence level and the margin of error you can accept.
How this calculator works
Sample size n = z squared x p x (1 – p) / e squared. For a known, smaller population N, the finite population correction n / (1 + (n – 1) / N) reduces the number you need.
Frequently asked questions
What sample size is common for surveys?
About 385 for 95% confidence and a 5% margin of error with a large population.
What if I do not know the proportion?
Use 50%, which gives the largest needed sample.
Does population size matter?
Only for small populations. Above about 100,000 it makes almost no difference.
