Margin of Error Calculator
Calculate the margin of error of a survey or poll from the sample size, proportion, and z-score.
Formula: MOE = z × √(p(1 − p) / n) × 100
About Margin of Error Calculator
Margin of Error Calculator is a free online calculator that gives you an instant, accurate result as you type. Calculate the margin of error of a survey or poll from the sample size, proportion, and z-score.
The calculation uses the standard formula MOE = z × √(p(1 − p) / n) × 100 and updates live with every change to the inputs. Everything runs client-side in your browser — fast, private, and free to use as often as you like.
The familiar "±3%" quoted in national polls comes from surveying roughly 1,000 people at a 95% confidence level.
Frequently Asked Questions
Is Margin of Error Calculator free to use?
Yes. Margin of Error Calculator is completely free, with no sign-up, no downloads, and no usage limits. You can use it as many times as you like on any device with a web browser.
How accurate is this calculator?
The calculator applies the standard formula (MOE = z × √(p(1 − p) / n) × 100) with full floating-point precision and rounds only the displayed result. For most practical purposes the results are exact.
Which z-score should I use?
Use 1.96 for 95% confidence (the default), 1.645 for 90%, and 2.576 for 99% confidence.
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