Guided calculators
Answer a few questions, get the number, the formula, and what it means.
Survey sample size
How many people do I need to estimate a percentage?
Not sure? Use 50%, which gives the largest (safest) sample.
How close you want your estimate to be, e.g. ±5%.
Leave blank for a large population.
385 respondents
Plan for more to allow for non-response (e.g. divide by your expected response rate).
n₀ = z²·p(1−p)/e², z = 1.96; finite: n = n₀ / (1 + (n₀−1)/N)