How to Use the T Distribution with T.DIST in Excel

Use T.DIST to get one-tailed p-values for small samples, such as testing whether batteries meet a claimed life.

You will learn to

• Find a left-tailed p-value from a t-score
• Compute the t-score inside the formula from sample data
• Find a right-tailed p-value

How it works

T.DIST works like NORM.S.DIST but for small samples, where the true standard deviation is unknown and has to be estimated. Its shape depends on the degrees of freedom — usually the sample size minus 1. =T.DIST(t,df,TRUE) returns the area to the left of t, which is the one-tailed p-value when you suspect the true mean is lower than claimed.

To test whether something is higher than claimed, use the right tail: 1-T.DIST(t,df,TRUE) or T.DIST.RT. A p-value below your significance level (often 5%) means the sample is unlikely if the claim were true.

=T.DIST(-1.9,14,TRUE)