Sample Size Calculator
Sample size for a survey or inspection at a chosen confidence level and margin of error.
Results
Sample size
385
Sample size
370
Percentage
3.70
%
What this tool does
Use z = 1.96 for 95 % confidence, 1.645 for 90 % and 2.576 for 99 %. If you have no idea what proportion to expect, leave it at 50 % — that is the worst case and gives the largest, safest sample. The finite population correction matters once your sample is a serious fraction of the whole group.
Formula
n = z² p (1−p) ÷ e² · corrected for a finite population
Variables
| Symbol | Meaning | Unit |
|---|---|---|
z | Z value (confidence) | — |
pp | Expected proportion | % |
er | Margin of error | % |
np | Population size | — |
N | Sample size | — |
NF | Sample size | — |
PC | Percentage | % |
Worked example
- Z value (confidence)1.96
- Expected proportion50 %
- Margin of error5 %
- Population size10,000
- Sample size385
- Sample size370
- Percentage3.70 %
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.