Free Sample Size Calculator
Determine the minimum sample size needed to achieve a desired margin of error at a given confidence level.
Sample Size (exact)
96.0400
Standard Error at This n1.5306
Sample Size (exact) vs Z-Value (e.g., 1.96 for 95%)
How to Calculate Required Sample Size
Formula
n = (z * sigma / E)^2
where E is the desired margin of error, z is the critical value for the confidence level, and sigma is the population standard deviation. Always round up to the next whole number since you cannot have a fractional observation.
Example Calculation
You want a 95% CI with margin of error 3 and estimated SD 15. How many observations are needed?
- 01n = (z * sigma / E)^2
- 02n = (1.96 * 15 / 3)^2
- 03n = (9.8)^2
- 04n = 96.04
- 05Round up: n = 97 observations needed
Frequently Asked Questions
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