This confidence interval calculator estimates the margin of error/accuracy of a survey by considering its sample & population sizes and a given percentage of choosing specific choice. Please note that a safe confidence interval is set to be between 3 and 5 %.

Confidence level:
Sample Size:*
Pick certain choice (%):*

What data you need to calculate the confidence interval

When assessing the level of accuracy of a survey, this confidence interval calculator takes account of the following data that should be provided:

  • Confidence level that can take any value from the drop down list: 50%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, 99.99%. Each confidence level from the ones provided above has its own Z score associated as detailed here:

- for confidence level 50% the Z Score is 0.67449;

- for confidence level 75% the Z Score is 1.15035;

- for confidence level 80% the Z Score is 1.28;

- for confidence level 85% the Z Score is 1.44;

- for confidence level 90%  the Z Score is 1.645;

- for confidence level 95% the Z Score is  1.96;

- for confidence level 97% the Z Score is 2.17009;

- for confidence level 98% the Z Score is 2.326;

- for confidence level 99% the Z Score is 2.576;

- for confidence level 99.99% the Z Score is 3.29053.

  • Sample size which is the number of people that will be interviewed.
  • Population that can be left blank if population in infinite or can be provided as a finite value;
  • Pick certain choice % refers to the percentage you expect people to pick up a certain choice from the possible answers.

Standard formulas used:

  • Margin of error formula:

Za/2 * σ/√(n)

  • State confidence interval equation:

x̅ ± Za/2 * σ/√(n)


x̅ = mean

Za/2 = confidence coefficient

a = confidence level

σ = standard deviation

n = sample size

13 Apr, 2015