Sample Size Calculator
Calculate survey sample size needed.
About this tool
Calculate how many people you need to survey to get results within a target margin of error, at a chosen confidence level \u2014 the standard formula used to plan surveys and polls.
Key Features
- 90%, 95% or 99% confidence levels
- Optional finite population correction for smaller populations
- Uses the conservative 50% proportion estimate by default
How to Use
- Choose your confidence level.
- Enter your target margin of error.
- Enter an estimated proportion (use 50% if unsure \u2014 it requires the largest sample, so it's the safe default).
- Optionally enter your total population size, if known and not very large.
- Click Calculate Sample Size.
Benefits
- Plan a survey or poll with a statistically sound sample size
- See how tightening your margin of error increases the required sample
- Adjust for a known, finite population
Frequently Asked Questions
50% produces the maximum possible variance in the sample size formula, meaning it requires the largest sample \u2014 using it as a default is the conservative, safe choice when you don't already know roughly what proportion to expect.
For very large or effectively infinite populations (like all adults in a country), population size barely affects the required sample. It matters more for smaller, finite populations (like employees at one company), where the finite population correction can meaningfully reduce the sample needed.