ffee
All tools
Margin of Error Calculator
Turn a survey sample size and result into a margin of error and a confidence interval.
Survey margin of error
Margin of error: —
Confidence interval: —
Standard error: —
Critical z value: —
How to use the Margin of Error Calculator
- Enter the number of people who answered your survey.
- Set the result you measured and, if you know it, the population size.
- Read the margin of error and confidence interval in the result panel.
Features
- Margin of error as a percentage
- Confidence interval for the proportion
- Optional finite population correction
- Runs locally, no uploads
Advertisement
Frequently Asked Questions
Common questions about the free online margin of error calculator.
Enter the sample size and the result you measured, choose a confidence level, and the margin
of error appears as a percentage.
At a 95 percent confidence level with a result near 50 percent, a sample of 1000 gives a
margin of error of about 3.1 percent.
Most surveys use 95 percent. A 99 percent level gives a wider margin of error, while 90
percent gives a narrower one.
When your sample is a large share of a small population, the correction shrinks the margin of
error because you sampled a big part of it.
A proportion of 50 percent gives the largest possible standard error, so it is the most
cautious assumption when the result is unknown.
It is the square root of the proportion times one minus the proportion, divided by the sample
size.
Yes. The margin of error falls with the square root of the sample size, so four times the
sample halves the margin of error.
It is the sample proportion plus or minus the margin of error, giving a range of plausible
values for the true proportion.
No. Every calculation runs locally in your browser, so your numbers never leave your device.
Yes. It is completely free and unlimited, with no account, no sign-up and no usage limits of
any kind.
Last updated: October 10, 2026