📊 Statistics
Sample Size Calculator
The required sample size depends almost entirely on how tight you want the estimate and how confident you want to be — not on how big the population is. That last part surprises people: a population of 100,000 and one of 100 million need nearly the same sample. The exception is small populations, where the finite population correction starts to matter.
How it works
Confidence level
Margin of error
Expected proportion
Population size (0 if unknown)
Required sample size
Before finite population correction
Correction factor
Responses for a 50/50 split at the same error
Frequently asked questions
How do I use the Sample Size 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.