Find how many people to survey for a given confidence level and margin of error, with an optional finite population correction. Enter your values; the result updates as you type, with the method shown below.
Formula
n₀ = z² p (1 − p) / e² n = n₀ / (1 + (n₀ − 1) / N)
Worked example
95% confidence, ±5%, p = 50%: 385 responses.
Frequently asked questions
Why use 50%?
It gives the largest, safest sample size when you do not know the proportion.
Does population size matter?
Only when it is small; above about 100,000 the answer barely changes.
Does this fix bias?
No, the sample must also be random.
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Results are estimates for information only. Check important figures with a professional.