Statistics calculator

Sample Size Calculator

Estimate survey sample size from confidence level, margin of error, and population proportion.

Formulan = z^2 x p x (1 - p) / e^2

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.

FAQ6 common questions for this calculator.

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?+

For the Sample Size Calculator, 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?+

For the Sample Size Calculator, enter confidence level, margin of error, and population proportion. Keep the units consistent with the calculator fields and compare your setup with the worked example on the page.

How accurate is the Sample Size Calculator?+

Sample Size Calculator calculates the selected statistic from the sample values provided. It uses the Proportion sample size, but missing data, outliers, sample bias, and distribution assumptions can affect what the result means.

What should I check before using the Sample Size Calculator result?+

For the Sample Size Calculator, check confidence level, margin of error, and population proportion, sample definition, missing values, outliers, and rounding precision. A statistic can be numerically correct but still describe a weak sample.

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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. 1

    Enter your details

    Enter confidence level, margin of error, and population proportion, then complete any other fields shown in the calculator.

  2. 2

    Check the calculation

    Review the result alongside the proportion sample size: n = z^2 x p x (1 - p) / e^2.

  3. 3

    Compare scenarios

    Change one or more inputs to see how they affect the sample Size Calculator result before you use the estimate.