📊 Statistics
Margin of Error Calculator
The margin of error is the plus-or-minus figure you see next to poll results. It shrinks with the square root of the sample size, so quadrupling your sample only halves the error. The confidence level decides how often the stated range is expected to contain the true value.
How it works
Sample size
Observed proportion
Confidence level
Population size (0 if unknown)
Margin of error
Lower bound
Upper bound
Standard error
Critical value (z)
Frequently asked questions
How do I use the Margin of Error Calculator?
Fill in the fields above — the result recalculates instantly as you type. Everything runs in your browser, so the values you enter are never collected or stored.
Is this calculator free?
Yes. It is completely free, requires no account, and works on phones, tablets and desktops.