Calculate confidence intervals for a mean, a proportion (Wilson and exact), the difference between two means or proportions, and odds ratios.
About this tool
Confidence intervals for means, proportions, differences, odds ratios and relative risks.
How to use Confidence Interval Calculator
- Choose what you need an interval for.
- Enter the summary figures or counts and pick the confidence level.
- Read the interval, with alternative methods for comparison.
Worked example
A mean of 120 with SD 15 from 50 people gives a 95% confidence interval of 115.74 to 124.26.
Which interval should I use for a proportion?
The Wilson score interval works well at all sample sizes. The simple Wald interval is unreliable when counts are small or near 0% or 100%.
Why use the t distribution for a mean?
With an estimated SD, the t distribution gives the correct width, especially for samples under about 30.
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