# Sample Size Calculator

 Confidence Level: 95% 99% Confidence Interval: %Enter Interval – e.g. 4 = 4% Population: Assumes a normal distribution of 50% to calculate your sample size

How to use the sample-size calculator

2. Enter your confidence interval – entered as a decimal
(e.g. 40% entered as .4)

Confidence Level: Tells how sure you can be. The most common percentages are 95% and 99%

Confidence Interval: The margin of error. How close your sample is to the true value of your population.

This calculator is used to determine how many individuals you need to survey in your research in order to gather results that reflect the target population as precisely as desired.

### Sample Size Formula

Where:
Z  = Z value (e.g. 1.96 for 95% confidence level)
p = percentage picking a choice, expressed as decimal
(.5 used for sample size needed)
c = confidence interval, expressed as decimal
(e.g., .04 = ±4)

(This calculator assumes a normal distribution of 50% when calculating your sample size)

To use this calculator, first choose your confidence level. This is the level of confidence in which  your data accurately represents the population.

Example: Choosing 95% = You are 95% certain your data is accurately reflected

Choosing 99% = You are 95% certain your data is accurately reflected

Next, you must enter your confidence interval. This is also known as your margin of error. Your confidence interval will appear as a positive and negative numerical value.

Example: When you enter a numerical value of 4, you are entering a confidence interval of 4%

So, if you use a confidence interval of 4% and 50% of your sample choose an answer, you can be “certain” that between 46% (50 – 4) and 54% (50 + 4) of the entire population from which the sample is pulled would choose the same answer.

Finally, you must input your desired population.

This is the number of people in the overall group your sample represents, such as the number of people in a city, the number of employees in your company, or  the total members of a national organization.