Quartile & IQR Calculator

This calculator finds the quartiles and interquartile range of a data set, and flags the boundaries beyond which values count as outliers. Quartiles split ordered data into four equal parts: the first quartile, Q1, is the 25th percentile, the second is the median, and the third quartile, Q3, is the 75th percentile. The interquartile range, or IQR, is the distance between Q1 and Q3, and it measures the spread of the middle half of the data, making it a robust gauge of variability that is not thrown off by extreme values the way the full range or even the standard deviation can be. The IQR also drives the standard rule for spotting outliers: any value more than 1.5 times the IQR below Q1 or above Q3 is flagged as a potential outlier, the same logic that draws the whiskers on a box plot. You paste or type your numbers, and the calculator returns Q1, the median, Q3, the IQR, the minimum and maximum, and the lower and upper outlier fences. The results update as you edit the data, so you can immediately see how an extreme value affects the spread and whether it falls outside the fences. Use it to summarise a dataset, to build or interpret a box plot, to detect outliers before further analysis, or for statistics homework. The quartiles use the standard interpolation method, consistent with most software. The calculations are exact for your numbers, rounded for display.

IQR is the spread of the middle half. Values beyond 1.5 x IQR past Q1 or Q3 are potential outliers (e.g. 95 here). Rounded for display.