Survey Margin of Error Calculator
Compute the margin of error and confidence interval of a survey proportion from sample size, observed proportion and confidence level.
How to Use the Survey Margin of Error Calculator
- Enter sample size.
- Enter the observed proportion in percent.
- Pick the confidence level.
- Click Calculate.
Use Cases
- •Reporting poll results.
- •Marketing research readouts.
- •Teaching inferential statistics.
Formula
E = Z × √(p(1−p)/n). Z = 1.645 (90%), 1.96 (95%), 2.576 (99%). For the most conservative estimate use p = 0.5.
Frequently Asked Questions
Why does 50% give the biggest error?
The variance p(1−p) is maximal at p = 0.5, so it is used as the worst-case default when the true proportion is unknown.
Finite population?
For small populations (N < 20·n) apply the finite-population correction factor √((N−n)/(N−1)); this calculator assumes a large population.