Call us at 1(800) 986-3004

Sample Size Calculator

How many people do you need to take your survey? Even if you’re a statistician, determining sample size can be tough. To make it easy, try our sample size calculator. We give you everything you need to to calculate how many responses you need to be confident in your results.

Population Size:
Confidence Level (%):
Margin of Error (%):
Sample Size:

What is a sample size?

The number of completed responses your survey receives is your sample size. It’s called a sample because it only represents part of the group of people (or population) whose opinions or behavior you care about. As an example, one way of sampling is to use a so-called “Random Sample,” where respondents are chosen entirely by chance from the population at large.

Understanding sample sizes

Here are a few key terms you’ll need to understand to calculate your sample size and give it context:

Population Size: The total number of people in the group you are trying to reach with your survey is called your population size. If you are surveying your patients, your population is the number of patients you see in a month. Similarly, if you are surveying your company, the size of the population is the total number of employees.

Confidence Level: A measure of how certain you are that your sample accurately reflects the population, within its margin of error. Common standards used by researchers are 90%, 95%, and 99%. Make an educated guess about the patients that respond to your survey requests...does it represent all of your patients, or is a segment (like elderly) missing? If it does represent all of your patients, choose a high confidence level (99%).

Margin of Error: A percentage that describes how closely the answers your sample gave is to the “true value” in your population. In other words, do you believe that the patients who have responded to your patient satisfaction surveys echo the opinions of ALL of your patients? The smaller the margin of error is, the closer you are to having the exact answer at a given confidence level. Five percent (5%) is a common margin of error.

As an example, say you need to decide if you can confidently make strategic business decisions based on your patient satisfaction responses. You have seen 1,000 patients over the last six months. If you decide that the "industry standard" of 5% margin of error at a 95% confidence level is appropriate, then you will need to get 278 completed surveys (or a 27.8% response rate).

Things to watch for when calculating sample size

  • A smaller margin of error means that you must have a larger sample size given the same population.
  • The higher your confidence level, the larger your sample size will need to be.

Tips for using the sample size calculator

If you are making comparisons between groups within your sample, you will need to take that into account when calculating sample size. If, for example, you break your sample out into two groups of equal size, your sample size for each group is cut in half and your margin of error will increase. This can make it difficult to make meaningful comparisons between groups in your survey.

Returning to the scenario from earlier, you have a population of 1,000 patients and you need 278 respondents to get to a 95% confidence level with a 5% margin or error. If you wanted to see how the opinions of women and men differ (presuming they each make up 50% of the sample), you would wind up with a sample size 139 (1/2 of 278 for each men and women) for a population of 500 (again, half of the total population estimate). With those numbers, your margin of error would go up—or you need to increase your sample size to 436 (218 men and 218 women).

Do you need more responses?

If the sample size calculator says you need more respondents, we can help. Give us a call!