Statistics

Sample Size Calculator

Choose how confident you want to be and how much error you can accept. If you're surveying a known, limited group, such as your 800 employees, enter its size to lower the number needed.

50% gives the largest, safest sample.

Your result will appear here.

How it's calculated

The base sample size comes from the z value for your confidence level, the expected proportion p and the margin of error e. For a limited population, the finite population correction shrinks it.

n₀ = z² × p × (1 − p) ÷ e² n = n₀ ÷ (1 + (n₀ − 1) ÷ N)

How to do it in Excel

=ROUNDUP(NORM.S.INV(0.975)^2*0.5*0.5/0.05^2, 0)
Returns 385 for 95% confidence and a 5% margin of error.