How to Use the Quartile & IQR Calculator
Quartiles and the IQR (interquartile range) are useful when you want to understand how your data is spread out and which values might be outliers. This calculator takes a list of numbers, sorts it, and computes Q1, Q2 (median), Q3, the IQR, and the lower and upper boundaries commonly used to flag outliers.
Q1 is the median of the lower half of the data, while Q3 is the median of the upper half. IQR is Q3 minus Q1, representing the range where the middle 50% of your data falls — the smaller the value, the more tightly clustered the data is.
In statistics, values below Q1 − 1.5×IQR or above Q3 + 1.5×IQR are typically flagged as outliers. Use this rule to spot unusual values in test scores, survey responses, or experimental data.
Frequently Asked Questions
After sorting the data, quartiles split it into four equal parts. Q1 is the median of the lower half, and Q3 is the median of the upper half.
IQR is Q3 minus Q1 — it represents the range where the middle 50% of the data falls.
Values below Q1 − 1.5×IQR or above Q3 + 1.5×IQR are commonly treated as outliers.