Quartile Calculator
Quartiles divide a sorted dataset into four equal sections. The first quartile (Q1) marks the 25th percentile, the second quartile (Q2) is the median at the 50th percentile, and the third quartile (Q3) marks the 75th percentile. This calculator finds all three quartiles from your data, displays the sorted dataset, and calculates the interquartile range (IQR), which measures the spread of the middle half of your data. Quartiles are essential for creating box plots, identifying outliers, and understanding data distribution.
Sorted data
Quartile formulas
Q1 = 25th percentile value
Q2 = 50th percentile value (median)
Q3 = 75th percentile value
IQR = Q3 - Q1
The data is sorted in ascending order. Q2 is the median. Q1 is the median of values below Q2. Q3 is the median of values above Q2.
Understanding quartiles
- Q1 (25%): 25% of values fall below Q1, and 75% are above it.
- Q2 (Median): 50% of values fall below Q2, and 50% are above it. Q2 is the center of the data.
- Q3 (75%): 75% of values fall below Q3, and 25% are above it.
- IQR (Interquartile Range): Contains the middle 50% of your data. Used in the 1.5 * IQR rule to identify outliers.
- Range: The difference between the maximum and minimum values in your dataset.
Quartile calculator: frequently asked questions
What are quartiles?
Quartiles divide a sorted dataset into four equal parts. Q1 (first quartile) is at 25%, Q2 (second quartile or median) is at 50%, and Q3 (third quartile) is at 75%. These three values split your data into four quarters, each containing roughly 25% of the data.
What is the difference between Q2 and the median?
Q2 and the median are the same thing. Q2 is the middle value when your data is sorted. If you have an odd number of values, Q2 is the middle value. If you have an even number, Q2 is the average of the two middle values.
What is the interquartile range (IQR)?
The interquartile range (IQR) is the difference between Q3 and Q1: IQR = Q3 - Q1. It represents the spread of the middle 50% of your data and is useful for identifying outliers and understanding data variability.
How do you calculate quartiles?
Sort your data in ascending order. Q2 is the median. Q1 is the median of the lower half of the data (below Q2). Q3 is the median of the upper half of the data (above Q2). There are several methods; this calculator uses the exclusive method (standard for most statistics software).
What are quartiles used for?
Quartiles are used to understand the distribution of data, create box plots, identify outliers, compare datasets, and summarize the spread and central tendency of data in a simple way.
Official sources
- NIST/SEMATECH e-Handbook of Statistical Methods: NIST Handbook.
- National Center for Education Statistics: NCES.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.