Sample Size & Margin of Error Calculator
Plan credible surveys with confidence. Enter a target population, choose your confidence level, and get the exact sample size you need—plus a visual preview of how accuracy changes as you collect more responses.
Survey Inputs
Adjust your assumptions to see how the sample size responds.
Leave blank for very large or unknown populations.
Higher confidence requires a larger sample size.
Most brand surveys aim for ±5%. Go tighter for executive decisions.
Stay at 50% for maximum uncertainty, or enter your best estimate.
We use this to estimate how many invitations you should send.
Results snapshot
Ready to brief your stakeholders or launch the survey.
https://www.fun-surveys.com/sample-size-calculator
How accuracy improves as sample size grows
Use this chart to explain diminishing returns to your team.
Quick insights
- The closer your expected responses are to a 50/50 split, the larger your sample should be.
- Doubling your sample size does not halve your margin of error—use the chart to show diminishing returns.
- Response rates under 20% are common for email surveys. Plan extra invitations to hit your quota early.
FAQ: Sample Size Planning
What if my population is very small?
When your population is small, we apply a finite population correction so the required sample size will never exceed the total number of people you can survey. You may end up surveying most of your audience.
Why is 95% confidence the default?
95% confidence is the market research standard. It balances speed and accuracy, letting you ship insights quickly without requiring thousands of extra responses.
How should I estimate my response rate?
Look at similar surveys you have run in the past, or start with a conservative 20–30%. You can always update the response rate later to see how many more invitations you need to send.
