Find the margin of error for a survey from its sample size, proportion, and confidence level. Enter the sample size and pick the confidence.
Usage Tip
To halve the margin of error, you need about four times the sample size.
The plus-or-minus around a survey estimate
It shrinks with larger samples and grows with higher confidence.
Choose the confidence level.
The margin assumes simple random sampling.
The margin of error describes how far a survey or sample result is likely to fall from the true value because of random sampling alone. It shrinks as the sample grows, but only with the square root of the sample size, so cutting the margin in half takes about four times as many responses.
The result only accounts for sampling variation. It says nothing about bias from a poorly chosen sample, badly worded questions, or people who did not respond. A narrow margin of error on a biased sample is still a misleading result, so check how the sample was collected before trusting the number.