Sample Size Calculator
Sample Size Formula
z : z-score
p : Population proportion
e : Margin of Error
N : Population size
Confidence Interval to z-Score
99% = 2.58
98% = 2.33
96% = 2.05
95% = 1.96
92% = 1.75
90% = 1.645
85% = 1.44
80% = 1.28
What is Sample Size?
Sample size is a measure used in statistics, often for research or surveys, to determine how many samples (or observations) would be needed in order to accurately reflect the population. When conducting research it is important to get a large enough sample that will represent the population. However, you also don't want too many samples due to the resources involved in reviewing the data (i.e. time and people).
Typically, prior to conducting research those involved with the project determine how large the population is that represents the particular task, or the area where the research would be applicable to what is being tested. Next they determine and acceptable level of margin of error to ensure their results are reliable and representative. Researchers will also want to establish a confidence level for the data being collected. The confidence level is the probability that the margin of error is accurate within the acceptable levels. You will also want to identify the percent, or proportion, of the population that will be applicable to the test.
Sample Size Video Tutorial
The following video provides an easy to understand overview of how to calculate sample size and what the variables mean. Note that it does start of slow, but it will help in understanding this concept.