Sizu Riatto
Statistics Didn’t Have to Be This Hard · Chapter 11

Confidence Interval

An average from a sample is an estimate. Enter the sample’s mean, standard deviation and size (or paste the data) to get a range that is likely to contain the true average.

Home › Calculators › Confidence Interval

Planning
Enter the mean, standard deviation and sample size, then press Calculate.
From the book, Chapter 11. Interval = mean ± t × (SD ÷ √n). Priya’s 25 battery packs (mean 9.4 h, SD 1.2 h) give 8.9 to 9.9 hours at 95%, with t = 2.064 for 24 degrees of freedom. The 95% describes the method: about 95 in every 100 intervals built this way contain the truth. It is not a range for single values.

Illustrative arithmetic only. Everything stays in your browser: no sign-up, nothing stored or sent.