Statistics
Sample Size Calculator
Use your desired confidence, margin of error, and response distribution to size surveys with or without a finite population.
Estimate how many responses you need for surveys or polls with margin of error and confidence tuning.
Sample size with finite correction
n₀ = (Z² × p(1 − p)) / E² n = n₀ / [1 + (n₀ − 1)/N]
Z is the critical value for the confidence level, p is the assumed response proportion, E is the margin of error, and N is the population (optional).
How to use
- Pick a confidence level to set the Z-score.
- Enter the acceptable margin of error and expected response distribution.
- Optionally add a population size to apply the finite population correction.
Example
Input: Confidence = 95%, Margin of error = 5%, Distribution = 50%, Population = 10,000
Output: Sample size ≈ 385 without population, ≈ 370 with finite correction
FAQ & notes
What response distribution should I use?
If you do not know the true proportion, use 50%. It produces the largest (safest) sample size requirement.
Can I model different confidence levels?
Yes—switch between 80%, 85%, 90%, 95%, or 99% confidence to see how the Z-score scales the required sample.