Formulas > Descriptive Statistics > Third Quartile

The third quartile (Q3) separates the bottom 75% of the sorted values of a data set from the top 25%.

For a data set , in which the values are sorted in increasing order,

Q3 = xi + a(xi+1 - xi)


where
i = floor(3(n+1)/4)
a = 3(n+1)/4 - i.