Sample Size Calculator (for Estimating a Mean)
Enter your estimated standard deviation, desired margin of error and confidence level to calculate the sample size needed.
Sample Size Calculator (for Estimating a Mean)
Calculate the minimum sample size needed to estimate a mean within a desired margin of error at a chosen confidence level.
This calculator provides an estimate for general informational purposes only. It is not a substitute for professional financial, mechanical or engineering advice.
This calculator rearranges the margin-of-error formula to solve for sample size, showing how many observations you need to hit a target precision at your chosen confidence level.
Example
- With the default values shown above, this calculator returns: Required Sample Size ≈ 96.
Frequently Asked Questions
What is the formula?
Required Sample Size = (z-score × Standard Deviation ÷ Desired Margin of Error)².
Where do I get an estimated standard deviation before collecting data?
Common approaches are using the standard deviation from a similar past study, running a small pilot sample first, or using a conservative (larger) estimate to be safe.