Margin of Error Calculator
Calculate the margin of error for surveys and polls.
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.
Can't find what you need?
Request a ToolHow to Use the Margin of Error Calculator
Select a confidence level, enter your sample size, and the observed or estimated proportion (default 50%). The calculator computes the margin of error using the formula ME = z * sqrt(p(1-p)/n).
About This Calculator
The margin of error quantifies the uncertainty in a survey result. A poll showing 52% support with a 3% margin of error means the true value is likely between 49% and 55%. Larger samples produce smaller margins of error. The margin of error applies only to random sampling error, not bias.
Frequently Asked Questions
What margin of error is acceptable?
For most surveys, 3-5% is considered acceptable. Political polls often target 2-3%. The acceptable level depends on the stakes of the decision being made.
Does the margin of error depend on population size?
For large populations, no. The margin of error depends primarily on sample size, not population size. For very small populations (under 5,000), a finite population correction can reduce it.
Why use 50% for proportion?
Using 50% gives the maximum (most conservative) margin of error. If you know the approximate proportion, using it will give a smaller, more accurate margin of error.