# Statistics > Sample Size > 1-Population Mean

This tool determines the sample size required to estimate a population mean. You will need to provide the confidence level, desired margin of error, and population standard deviation. The sample size is computed using the following formula:

where zα/2 is the inverse cumulative probability of the z distribution at 1 - &alpha/2, σ is the population standard deviation, and E is the margin of error.

To use this tool, provide the following inputs to the dialog:

- Confidence Level: a number between 0 and 1. For example, enter 0.95 for a 95% confidence level.
- Standard Deviation: the population standard deviation.
- Margin of Error: the desired margin of error.