Calculate the sample size you need for a survey or study to achieve a target margin of error at your chosen confidence level — essential for polling and market research.
How it works
- Set the desired confidence level (typically 95%).
- Input the acceptable margin of error as a percentage.
- Specify expected proportion (default to 50%) to see the exact sample size needed.
Frequently asked questions
Why use 50% as the proportion?
It produces the maximum required sample size, giving a safe estimate when you do not know the true proportion in advance.
Does population size matter?
For large populations (over ~20,000), it barely changes the result. For small populations, apply a finite population correction to reduce the required sample.
What is a typical survey sample size?
National polls often use ~1,000 respondents for roughly a 3% margin of error at 95% confidence.