Quartile Calculator
Find the first, second (median), and third quartiles of a data set.
Find the first, second (median), and third quartiles of a data set.
How Quartile Calculator Works
After sorting the data, quartiles mark the 25%, 50%, and 75% points through the list — Q2 is simply the median, while Q1 and Q3 mark the midpoints of the lower and upper halves respectively.
Who Uses Quartile Calculator and Why
- Finding the exact Q1, median, and Q3 values needed to construct a box plot by hand.
- Summarizing the shape of a data set at a glance before deciding on further statistical analysis.
- Comparing the quartile values of two or more data sets side by side to see where their distributions differ.
Mistakes to Avoid
- Assuming quartiles are always exact values that appear in the original data set — when a quartile position falls between two data points, interpolation is used, so the result can be a value not literally present in your data.
- Expecting an identical result from every statistics tool or spreadsheet — several accepted interpolation methods exist for computing quartiles, and different software defaults to different ones.
- Forgetting that Q2 is simply the median — computing it separately with a different method than Q1 and Q3 can introduce needless inconsistency.
Tips for Best Results
- If you're cross-checking this result against Excel or another statistics package, expect small differences for data sets where a quartile falls between two points — this comes down to the interpolation method, not an error.
- Use this calculator's Q1/Q3 output directly with the IQR Calculator if you also need the interquartile range in one pass.
Fixing Common Problems
My Q1 or Q3 value doesn't match what Excel calculated. — This calculator uses linear interpolation, a widely used method, but Excel and other statistics packages sometimes default to a different interpolation convention — small discrepancies for the same data set are expected and not necessarily an error.
Terms Explained
Quartile: One of three values (Q1, Q2, Q3) that split a sorted data set into four equal parts.
Linear interpolation: A method of estimating a value that falls between two known data points by proportionally blending between them.