Statistics
Sample Size Calculator
Use this sample size calculator to plan surveys and proportion estimates before collecting data.
Required sample size
—
- Z critical value
- —
Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the sample size calculator solves
Use this sample size calculator to plan surveys and proportion estimates before collecting data.
Formula
How to use it
- Choose confidence level.
- Enter margin of error.
- Use 50% expected proportion if unsure.
How to read the answer
Smaller margins of error and higher confidence require larger samples. The result is a planning estimate for proportions, not a guarantee that the final survey will be unbiased.
Common mistakes and edge cases
- This is for proportions, not means.
- Biased sampling cannot be fixed by larger sample size.
- Finite population correction is not included.
Worked examples
Common survey setup
Required sample size
385
Tighter margin
Required sample size
1,068
Frequently asked questions
Why does 50% give the largest sample?+
p(1-p) is largest at p = 0.5, so it is conservative.
Does population size matter?+
For very small populations, a finite population correction can reduce the required sample. For large populations, confidence level and margin of error usually matter much more.
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Last updated: May 8, 2026