Quartile & IQR Calculator
Calculate Q1, Q2, Q3, and interquartile range for any dataset.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
Can't find what you need?
Request a ToolHow to Use the Quartile & IQR Calculator
Enter your data separated by commas or spaces. The calculator sorts your values and computes Q1 (25th percentile), Q2 (median), Q3 (75th percentile), and the interquartile range (Q3 minus Q1). The IQR measures the spread of the middle 50% of your data, making it resistant to outliers.
About Quartiles and IQR
Quartiles divide sorted data into four equal parts. The IQR captures the range of the central half of data points. It is commonly used to build box plots and to identify outliers (values below Q1 - 1.5*IQR or above Q3 + 1.5*IQR). Unlike range or standard deviation, the IQR is not affected by extreme values, making it a robust measure of variability.
Frequently Asked Questions
How is IQR used to find outliers?
Any value below Q1 - 1.5 * IQR or above Q3 + 1.5 * IQR is considered a mild outlier. Values beyond 3 * IQR from the quartiles are extreme outliers. This is the method used in box-and-whisker plots.
What is the difference between IQR and range?
Range uses the minimum and maximum, so one outlier can make it very large. IQR only considers the middle 50%, making it robust to extreme values at either end.
Are there different methods for calculating quartiles?
Yes. The inclusive method, exclusive method, and linear interpolation method can give slightly different results, especially with small datasets. This calculator uses linear interpolation, which is the most common method in modern statistics software.