Sample Size Calculator
How many people do you need to survey?
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Sample Size Calculator by TheCalcTools
How the Sample Size Calculator works
Choose how precise you want the result to be (margin of error) and your confidence level.
Enter the expected proportion, or 50% if you do not know.
Optionally enter the population size to apply the finite population correction.
The formula
Worked example
Using the default values shown in the calculator:
| Desired margin of error (± %) | 5 |
|---|---|
| Expected proportion (%) | 50 |
| Confidence level | 95% |
| Population size (0 for very large) | 0 |
- n₀ = 1.96² × 0.5 × 0.5 ÷ 0.05² = 384.16.
- Rounded up, the sample size is 385.
- For a population of 1,000 the corrected size would be 278.
Result:
| Sample size, infinite population | 385 |
|---|---|
| Sample size, adjusted for population | 385 |
Frequently asked questions
What if I don't know the proportion?
Use 50%. It gives the largest sample size, so you will have enough data whatever the true value is.
Why does a small population need fewer respondents?
Sampling a big share of a small population gives more information per response, so the finite population correction reduces the required number.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.