Using the Sample Size Calculator
Enter the expected proportion as a percentage. A 50% assumption gives the largest variance for this simple proportion model, making it a common planning choice when the proportion is unknown.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- Margin of error (%)
- 5
- Expected proportion (%)
- 50
- Population (0 for unlimited)
- 0
- Confidence level
- 95%
Example result
- Required sample size
- 385
Method and assumptions
n₀ = z²p(1−p)/e², with a finite-population correction when a population is provided.
Check what the data represents
A statistical result is only meaningful in relation to the observations and assumptions behind it. Keep track of whether values describe a whole population or a sample, whether observations are independent, and which distribution the method uses. More decimal places cannot compensate for a sample that does not represent the question you are trying to answer.
Common question
What should I enter for an effectively unlimited population?
Use zero in the population field. The calculator then uses the uncorrected proportion sample-size formula rather than the finite-population adjustment.
Guide updated .