Sample Size Calculator
Enter the SD, desired margin of error, and confidence.
Result
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Enter numbers to see the result.
Unrounded n
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Rule
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Formula: n = (z x sigma / E)^2, always rounded UP to the next whole person.
Find the required sample size for a target margin of error, given the SD and confidence level.
Enter the SD, desired margin of error, and confidence.
Enter numbers to see the result.
The margin of error is E = z sigma / sqrt(n). Solving for n gives n = (z sigma / E)^2. With sigma = 10, E = 2, and 95% confidence: (1.96 x 10 / 2)^2 = 96.04, which rounds up to 97 people.
Rounding down would give a slightly larger error than requested, so the tool always rounds up to the next whole sample. Unknown sigma? Run a small pilot study first, or use 0.5 for proportions as the conservative choice.