Survey Sample Size Calculator
Find out exactly how many responses you need for statistically valid results. Set your confidence level and margin of error.
Configure your survey parameters
Leave population size empty if your audience is very large or unknown (the calculator uses an infinite population assumption).
The total number of people in your target group.
How confident you want to be that your results reflect the true population. 95% is the industry standard.
How much error you're willing to accept in your results. ±5% is commonly used.
Now that you have your target, start reaching them.
Create your survey on SurveyReflex and collect exactly the responses you need — no subscriptions required.
Understanding Sample Size
Confidence Level
The probability that your results accurately reflect the population. A 95% confidence level means if you ran the survey 100 times, 95 results would fall within your margin of error.
Margin of Error
The range within which the true population value is expected to fall. A ±5% margin means your results could differ by up to 5 percentage points from the true value.
Population Size
The total group you want to study. For large or unknown populations, the sample size converges — beyond ~100,000, adding more people barely changes the required sample.
Why p = 50%?
This calculator uses a 50% response distribution — the most conservative assumption. It produces the largest (safest) sample size, giving you valid results regardless of how opinions are split.
Formula (Cochran's)
n = (Z² × p × (1 − p)) / e²With finite population correction: n = n₀ / (1 + (n₀ − 1) / N)