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Quartile Calculator

Calculate Q1, Q2, Q3, and IQR with multiple methods

Calculator
Statistics
Mathematics
Data Analysis

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About This Tool

The Quartile Calculator computes the first quartile (Q1), second quartile (median/Q2), third quartile (Q3), and interquartile range (IQR) for any dataset. It supports three different calculation methods so you can see how the choice of method affects your results.

Quartiles are essential descriptive statistics that divide your data into four equal parts, revealing the distribution and spread of values. They form the basis of box plots (box-and-whisker plots) and are widely used in exploratory data analysis, quality control, educational assessment, and scientific research.

You can also use our Five Number Summary Calculator for a combined view including min, max, and outlier detection, or our Coin Flip Probability Calculator for probability distributions. For sorting and organizing data, try our Find & Delete Duplicate Lines.

Browse more Statistics tools for additional data analysis and probability calculators.

All processing happens in your browser — no data is sent to servers.

Frequently Asked Questions (FAQ)

What is a quartile?
A quartile divides a sorted dataset into four equal parts. Q1 (first quartile) separates the lowest 25% of data from the rest. Q2 (second quartile or median) splits the data in half. Q3 (third quartile) separates the highest 25% of data. The difference between Q3 and Q1 is the interquartile range (IQR), which measures the spread of the middle 50% of the data.
What is the difference between quartile calculation methods?
Tukey's method (inclusive) includes the median in both halves when n is odd. Moore & McCabe's method (exclusive) excludes the median from both halves. The interpolation method uses linear interpolation between data points based on percentile positions. Different methods can produce slightly different Q1 and Q3 values, especially with small datasets.
What is the interquartile range (IQR) used for?
The IQR is used to measure statistical dispersion and identify outliers. Values more than 1.5 × IQR below Q1 or above Q3 are considered potential outliers. You can use our Five Number Summary Calculator for a more complete analysis including outlier detection.
Which quartile method should I use?
Tukey's method is the most common and is widely used in introductory statistics and box plots. Moore & McCabe's method is common in AP Statistics. Interpolation is often used in scientific computing and software packages. For most use cases, Tukey's method is recommended.
How do you find Q1 and Q3 with an even number of data points?
With an even dataset, the median falls between two values (the average of the two middle numbers). The lower half is the left half of the data (excluding the median), and Q1 is the median of that lower half. Q3 is the median of the upper half. This applies to both Tukey and Moore & McCabe methods.
Is my data processed securely?
All calculations happen entirely in your browser. No data is sent to any server. Your calculation history is stored locally on your device using localStorage.

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