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Sample Size Calculator

Calculate the survey sample size needed from confidence level, margin of error and proportion.

385

respondents needed

Use 50% for the proportion when unsure — it gives the largest, safest sample size.

How to use it

  1. Pick a confidence level Usually 95%.
  2. Set the margin of error How precise you need the result, as a percent.
  3. Add the population Optional, to correct for a small population.

Examples

95%, 5%, p=50% 385
+ population smaller

About this tool

Run a survey with too few people and the results are meaningless; too many and you waste effort. This calculator finds the sample size you need from your confidence level, the margin of error you can accept and the expected response proportion.

It uses the standard formula for estimating a proportion and includes an optional finite-population correction for smaller groups. When you don’t know the likely split, 50% gives the safest, largest sample. Everything runs in your browser.

Frequently asked questions

Why does the proportion matter?

The required size depends on the expected response split. 50% gives the largest, most conservative sample, so use it when you're unsure.

When do I need the population size?

For small or finite populations, the correction reduces the required sample. For large populations it barely changes the result.

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Updated June 15, 2026