Sample Size to Achieve Desired Error Rate
Use this calculator to determine how many surveys you need to achieve a desired confidence interval (or margin of error). A confidence interval, or margin of error, tells you the range that likely contains the true value of a population. You may have seen it as a plus or minus amount reported with poll results. For example, if your confidence interval is 6, and 70% of your sample picks an answer, you can be sure that if you asked everyone in the population, you would get an answer of between 64% and 76% (70% ± 6%).
N [universe]: The total number of people your sample represents
Confidence Level: A confidence level tells you how often the true percentage of the population falls within the confidence interval. Using a 95% confidence level means you can be 95% certain, and a 99% confidence level means you can be 99% certain that the true percentage of the population is within the confidence interval.
Picking a higher confidence level means your confidence interval will be larger. Picking a lower confidence level means the confidence interval will be smaller.
If you don’t know what to pick, a 95% confidence level is commonly used.
|z [confidence interval in decimal form]|
|e [desired error]|
|n [Sample Needed]|