Sample Size Estimator -- Determining Sample Size


There are several formulas you can use to determine the sample size needed to statistically represent a population. Which one you use depends on what information you know and how you plan to report the results of your study.

     1. Use a proportions-based formula if you plan to report results as percentages (proportions) of respondents.
     2. Use a means-based formula if you plan to report results as means (averages) of respondents.
     3. Use the general formula if you cannot estimate the percentage or standard deviation of the attribute of interest.

Some values below are preset. You may accept them (by bypassing) or change them as desired

Population size from which the sample will be drawn (between 1 and 1000000 -- no commas):

Percentage of the population (1 to 99) possessing the attribute of interest? (for Proportions formula):

Standard Deviation of the attribute of interest in the population? (for Means formula):

Select an accuracy (precision) level: .01 [very high precision] .05 [high precision] .10 [low precision]

Select a confidence level: .95 .99

If you plan to survey the sample, enter expected percent return rate (between 1 and 100). If not, enter 100:

Compute sample size using one of these formulas:

to reset values           when finished