Proportion Sample Size Calculator
Proportion Sample Size with explicit assumptions and reproducible inputs.
Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Simple random sampling, normal approximation, no nonresponse/design-effect adjustment. This is precision planning, not a hypothesis-test power calculation.
Example Calculation
- Desired absolute margin: 0.05 fraction
- Confidence level: 95 %
- Planning proportion p: 0.5
- Population size (0 = unbounded): 0
95% confidence, margin0.05 and p0.5 need 385 observations for an unbounded population.
Method references
Frequently asked questions
How do I use this calculator?
Enter desired absolute margin, confidence level, planning proportion p, population size (0 = unbounded). The result updates automatically. Use Reset to restore the example values.
What method does it use?
n₀=z²p(1−p)/e²; finite population: n=n₀/[1+(n₀−1)/N]; round up.. Simple random sampling, normal approximation, no nonresponse/design-effect adjustment. This is precision planning, not a hypothesis-test power calculation.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.