Sample Size Calculator
Determine how many responses you need for statistically valid results.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Sample Size Calculator
Select your desired confidence level, enter the acceptable margin of error (as a percentage), and the estimated proportion (use 50% for maximum sample size). Optionally enter the population size for finite population correction.
About This Calculator
Sample size calculations ensure your survey or study has enough responses to produce statistically valid results. The formula balances the desired precision (margin of error) with the confidence level and expected variability. Using 50% as the estimated proportion gives the most conservative (largest) sample size.
Frequently Asked Questions
Why does 50% proportion give the largest sample size?
Because p(1-p) is maximized when p = 0.5. This means maximum variability, requiring the largest sample to achieve the same margin of error.
What if I do not know the estimated proportion?
Use 50%. This gives the most conservative estimate and ensures your sample is large enough regardless of the true proportion.
Does population size matter?
For large populations (over 20,000), the required sample size is essentially the same. For smaller populations, the finite population correction reduces the needed sample.