When you carry out a survey, you try to interview a relatively small group of people relative to the whole population size. Nonetheless, you want to estimate what percentage of the whole population would give a particular answer to the question you asked. The approximated 95% confidence interval gives you an idea of the reliability of your survey. If you did this survey many times, each time interviewing the same total number N of people, but choosing those people at random from the population every time, then you would find that the ratio (number of people who gave answer A)/ (number N of people interviewed) would not be the same every time. The 95% confidence interval gives you a central value and upper and lower bounds within which the ratio would fall 95% of the times you conducted the interviewing experiment.

Here you can calculate the 95% confidence interval of a survey. Enter the appropriate values into the entry windows, and then click the button to calculate the approximated 95% confidence interval.

The sample proportion is the percentage of people, among all those interviewed, who gave one particular answer. Enter integer percentage here.

The sample size is the number of people who were interviewed.

Confidence Interval Calculator