Quartile Calculator

About this calculator

Quartiles split an ordered data set into four equal-sized groups: Q1 (the first quartile) is the value below which about a quarter of the data falls, Q2 is the median, splitting the data in half, and Q3 (the third quartile) is the value below which about three-quarters of the data falls. The interquartile range, IQR = Q3 − Q1, measures the spread of the middle 50% of the data, ignoring the extremes at either end.

Statisticians and data analysts use quartiles constantly to summarize a distribution without being thrown off by outliers the way a mean can be — the box-and-whisker plot is built directly from Q1, the median, and Q3, and the common ‘1.5 × IQR’ rule flags any point more than 1.5 interquartile ranges below Q1 or above Q3 as a potential outlier worth a closer look.

Enter a list of numbers and the calculator sorts the data and returns Q1, Q2 (the median), Q3 and the interquartile range.