Sample Size Calculator
Enter the confidence level, margin of error and expected proportion — you will get the sample size, i.e. how many people to ask for the survey. If you enter a population, the finite population correction is applied too.
How to use
- Choose the confidence level (usually 95%).
- Write the margin of error in percent, for example 5 means ±5%.
- If you do not know the proportion, keep it at 50 — this gives the safest (largest) sample.
- If you know the total population, enter it too.
Note: Formula (Cochran): n₀ = z² x p(1-p) / e², then the population correction n = n₀ / (1 + (n₀ - 1)/N). Sample size is always rounded up (ceil). This is only an estimate; the actual survey design matters too.
Frequently Asked Questions (FAQ)
What do I need to enter?
Confidence level (usually 95 percent), margin of error in percent, and the expected proportion. If you know the total population, enter it for the finite population correction.
What if I do not know the expected proportion?
Keep it at 50 percent. That gives the safest, largest sample size.
What is the finite population correction?
If you enter the total population, the tool applies the finite population correction from the Cochran formula, which slightly reduces the required sample for small populations.
Is the sample size rounded?
Yes. The result is always rounded up to the next whole person, since you cannot survey a fraction of a person.
What does the result mean?
The number of people you need to survey for your chosen confidence level and margin of error.