Calculate a Sample Size from a Mean & Standard Deviation

This calculator will determine the required size of a sample for research questions involving means and the standard deviation.

Four questions must be answered to determine the sample size:

1. Desired confidence level (%): The confidence level is your level of certainty that the sample mean does not differ from the true population mean by more than the maximum acceptable difference. Typically, social science research uses a 95% confidence level.
2. Size of the population you will be sampling from. 20,000 is the maximum – anything above that number makes no difference.
3. Standard deviation of the population: Typically, the standard deviation of the population is estimated from the results of a previous survey, from a pilot study, from secondary data, or the client organization’s knowledge of the population as well as an estimate from the researcher.
4. Mean score: Like the standard deviation, this score can be estimated from a previous study, a pilot study, secondary data or estimates by the client or researcher.