Sample size guide

How to use the Sample Size Calculator

The Sample Size Calculator estimates how many responses you need for a proportion survey based on confidence level, margin of error, and expected proportion.

Open the sample size calculator

Quick start

Choose a confidence level.
Enter the margin of error as a percentage.
Enter the estimated population proportion, often 50% when unknown.
Add a finite population size only when the population is limited.

What the inputs mean

Higher confidence levels usually require a larger sample. Smaller margins of error also require a larger sample.

The estimated proportion is the expected percent of people with the answer or trait you are measuring. If you do not know it, 50% is the conservative default.

Finite population correction

If the total population is small and known, enter it to apply a finite population adjustment.

If the audience is very large or unknown, leave population size blank and use the standard large-population estimate.

Examples from the calculator

Common survey 95%, 5% margin, 50% proportion

385

Finite population 95%, 5%, 50%, population 1,000

278

Higher confidence 99%, 5%, 50%

664

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