Sample Size Calculator
Determine the required sample size for your survey or study. Calculate how many responses you need for statistically significant results.
Inputs
Results
Required Sample Size
385
How to Use This Calculator
- Enter the desired Confidence Level (e.g., 95%) and Margin of Error (e.g., 5%) for your survey.
- The calculator uses the formula n = z² × p(1−p) / e², where z is the critical z-score and p is the estimated proportion.
- If you have a prior estimate of the response proportion, enter it; otherwise use 0.5 (maximum variability, largest required sample).
- For a finite population, enter the Population Size and the calculator applies a finite population correction factor.
- A larger margin of error requires fewer respondents; halving the margin of error quadruples the required sample size.
- Results are rounded up to the nearest integer since you cannot survey a fraction of a person.
How the result changes with Margin of Error
| Margin of Error | Required Sample Size |
|---|---|
| 5.09% | 371 |
| 18% | 30 |
| 33% | 9 |
| 45% | 5 |
What each input means
- Confidence Level
- How confident you want to be in your results
- Margin of Error
- Acceptable range of error (e.g., ±5%)
- Expected Response Rate
- Use 0.5 if unknown (most conservative)
- Population Size
- Total population size (0 for infinite/unknown)
What each result means
- Required Sample Size
- For infinite population
- Adjusted Sample Size
- Adjusted for finite population
How this is calculated
Formula
n = (z² × p × (1-p)) / e²Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.
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