Sample Size Calculator

Determine the required sample size for surveys and statistical studies.

Result

Fill in the fields above, then press Calculate.

A sample size calculator determines how many observations you need for statistically significant survey or experiment results.

Select the desired confidence level, enter the margin of error (as a percentage), population proportion, and optionally the total population size. The calculator determines the minimum sample size needed.

Examples

General survey

95% confidence, 5% margin, 50% proportion: n = 1.96² × 0.5 × 0.5 / 0.05² = 385

Small population

Same parameters with population 500: n = 385 / (1 + 384/500) = 218

Tight margin

99% confidence, 2% margin: n = 2.576² × 0.25 / 0.0004 = 4,148

Frequently Asked Questions

Why use 50% for population proportion?
Using 50% gives the maximum (most conservative) sample size. If you have prior knowledge about the proportion, use that for a potentially smaller required sample.
What is the finite population correction?
When sampling from a limited population, the required sample size can be reduced. The correction adjusts for the fact that sampling a larger fraction of the population provides more information.
How does margin of error affect sample size?
Halving the margin of error roughly quadruples the required sample size, since E appears squared in the denominator.
Related Calculators
Confidence Interval Calculator
P-Value Calculator
Z-Score Calculator
Probability Calculator

Quick Tips

  • •Double-check your inputs — small errors lead to incorrect results.
  • •Use 50% for population proportion when you have no prior estimate, as it gives the most conservative sample size.
  • •Specify the population size for small populations to benefit from the finite population correction.