What response distribution should I use?
If you do not know the true proportion, use 50%. It produces the largest (safest) sample size requirement.
Step-by-step walkthrough
Sample Size Calculator Guide
Use this companion guide beside the interactive calculator to make sure you understand the “why” behind every click. Each section includes the classroom explanation, student-friendly language, and quick practice prompts.
Before you start
Collect the data points listed below and double-check their units. Keeping an organized “givens” list is one of the fastest ways to reduce math errors and impress exam graders.
- sample size
- margin of error
- confidence level
Detailed procedure
Step 1
Pick a confidence level to set the Z-score.
Step 2
Enter the acceptable margin of error and expected response distribution.
Step 3
Optionally add a population size to apply the finite population correction.
Teaching & troubleshooting tips
Can I model different confidence levels?
Yes—switch between 80%, 85%, 90%, 95%, or 99% confidence to see how the Z-score scales the required sample.