Margin of Error: n = 400, p = 0.5, 95% Confidence
With 400 survey responses and p = 0.5, the 95% confidence margin of error is ±4.9%, just under 5%.
How to use this tool
- Enter sample size (n), proportion (p) and z* (confidence level) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your margin of error and the full breakdown beneath it.
Calculate the margin of error for a 400-respondent survey, a common sample size for regional or niche polls.
Frequently asked questions
- What is the margin of error?
- The margin of error quantifies the uncertainty in a sample proportion estimate. A MOE of ±3% at 95% confidence means the true proportion is within 3 percentage points of the observed proportion 95% of the time.