Sample Size Calculator
Determine the minimum sample size needed for a survey or study based on your desired confidence level and margin of error.
Use 0.5 if unknown (gives largest sample size)
e.g. 0.05 = ±5%
About Sample Size Calculation
The required sample size depends on three factors: the confidence level (how certain you want to be), the margin of error (how precise your estimate needs to be), and the expected proportion of the population with the characteristic you're measuring.
Why p = 0.5?
When you have no prior estimate of the proportion, using p = 0.5 maximizes p(1−p) and thus gives the largest (most conservative) sample size. This ensures your results will be valid regardless of the true proportion.
Finite Population Correction
This calculator assumes an infinite (very large) population. If your population is small, apply the finite population correction: n_corrected = n / (1 + (n−1)/N), where N is the population size.
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For a related calculation, use Probability Calculator to calculate probabilities for single events, two independent events, and conditional probability. Alternatively, use Mean, Median, Mode, Range Calculator to calculate mean, median, mode, and range with step-by-step working. Great for students.
For the underlying method, read A Practical Guide to Statistical Sample Size: How Many People Do You Actually Need to Survey?.