## Sample size calculator

 What margin of error can you accept? 5% is a common choice % What confidence level do you need? Typical choices are 90%, 95%, or 99% % What is the population size? If you don't know, use 20,000 What is the response distribution? Leave this as 50% % Your recommended sample size is 377

## Sample Size Calculator Notes

• Margin of Error

The margin of error is the amount of error that you can tolerate. If 90% of respondents answer yes, while 10% answer no, you may be able to tolerate a larger amount of error than if the respondents are split 50-50 or 45-55.

Lower margin of error requires a larger sample size.

• Confidence Level

The confidence level is the amount of uncertainty you can tolerate. Suppose that you have 20 yes-no questions in your survey. With a confidence level of 95%, you would expect that for one of the questions (1 in 20), the percentage of people who answer yes would be more than the margin of error away from the true answer. The true answer is the percentage you would get if you exhaustively interviewed everyone.

Higher confidence level requires a larger sample size.

• Population Size

How many people are there to choose your random sample from? The sample size doesn't change much for populations larger than 20,000.

• Response Distribution

For each question, what do you expect the results will be? If the sample is skewed highly one way or the other,the population probably is, too. If you don't know, use 50%, which gives the largest sample size.

• Recommended Sample Size

This is the minimum recommended size of your survey. If you create a sample of this many people and get responses from everyone, you're more likely to get a correct answer than you would from a large sample where only a small percentage of the sample responds to your survey.

• Script for calculator provided by Raosoft.com

## Margin of Error Calculator

 Population Size Sample size Margin of error (+/-)

## Margin of Error Calculator Notes

• Enter a population size and a sample size to calculate the theoretical margin of error, plus or minus in percentage points, 95% of the time, on questions where opinion is evenly split.