Statistics calculator
Sample Size Calculator
Estimate survey sample size from confidence level, margin of error, and population proportion.
Formula
Proportion sample size
This is a general planning estimate and does not account for survey design effects or response bias.
n = z^2 x p x (1 - p) / e^2
95% confidence, 5% margin, and 50% proportion needs about 385 responses.
FAQs
Why is 50% often used for proportion?+
It is the most conservative choice when the expected proportion is unknown.
Does population size matter?+
This simple version does not apply finite population correction.
How does the Sample Size Calculator calculate the result?+
It uses the Proportion sample size: n = z^2 x p x (1 - p) / e^2. 95% confidence, 5% margin, and 50% proportion needs about 385 responses.
What information do I need to use the Sample Size Calculator?+
Estimate survey sample size from confidence level, margin of error, and population proportion.
How accurate is the Sample Size Calculator?+
Sample Size Calculator applies the formula and assumptions shown on this page. Results may be rounded for readability, so verify changing rates, thresholds, medical guidance, or legal rules with the cited source or a qualified professional.
What should I check before using the Sample Size Calculator result?+
Check that the units, dates, rates, and assumptions match your situation. Change one input at a time to understand which values have the largest effect on the result.
Statistics guide
How to use the Sample Size Calculator
Estimate survey sample size from confidence level, margin of error, and population proportion. The page also explains the proportion sample size and shows a practical example: 95% confidence, 5% margin, and 50% proportion needs about 385 responses.
- 1
Enter your details
Enter confidence level, margin of error, and population proportion, then complete any other fields shown in the calculator.
- 2
Check the calculation
Review the result alongside the proportion sample size: n = z^2 x p x (1 - p) / e^2.
- 3
Compare scenarios
Change one or more inputs to see how they affect the sample Size Calculator result before you use the estimate.
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