Sample size calculator for needs assessments and KAP surveys

The following calculator will help you find an appropriate sample size for a needs assessment survey, a KAP survey, or any other kind of survey intended to provide a "snapshot" of a population at a given point in time. The results of the survey can be used to draw conclusions about the population as a whole, and can provide useful inputs on the design and planning of interventions. To measure change over time in the same population, see our Baseline and endline sample size calculator.

Measuring a percentage

You can expect results like:


This calculator uses the following formula to find the required sample size:

$$ n=\frac{m}{1+\frac{m-1}{N}} $$

Where \(m\) is the sample size required for a large population, and \(N\) is the actual population size.

The required sample size for a large population is:

$$ m=\frac{z^2_{\alpha/2}\hat{p}(1-\hat{p})}{\epsilon^2} $$

Where \(\hat{p}\) is the expected proportion in the population, \(\epsilon\) is the allowable margin of error, and \(z^2_{\alpha/2}\) is the z-Score that corresponds to the 95% confidence level.

For a proof of this formula, see Penn State's excellent Introduction to mathematical statistics course.