How to use this quartile calculator
Paste your dataset above and press Calculate. You will get Q1, the median (Q2) and Q3 (calculated with the same linear-interpolation method Excel's QUARTILE.INC uses) plus the interquartile range they define.
What are quartiles?
Quartiles cut a sorted dataset into four equal parts. The first quartile (Q1) is the 25th percentile: a quarter of values fall below it. The second quartile is the median. The third quartile (Q3) is the 75th percentile. Between Q1 and Q3 sits the middle half of your data, the part that represents "typical", while the extremes live in the outer quarters.
Quiz scores for a class of ten: 58, 72, 65, 80, 91, 67, 72, 74, 69, 72. Sorted: 58, 65, 67, 69, 72, 72, 72, 74, 80, 91. The calculator gives Q1 = 67.5, median = 72, Q3 = 73.5. Read it as a story: a quarter of the class scored under 67.5, half scored 72 or less, and three-quarters were done by 73.5: a tight, consistent class with one star (91) and one straggler (58) stretching the ends.
A warning about methods
There are several legitimate ways to place quartiles in a small dataset (inclusive, exclusive, Tukey hinges), and different tools can give slightly different answers for the same numbers. This calculator uses linear interpolation: Excel's QUARTILE.INC and the most common textbook approach for software. If your teacher's method differs, your hand answer may differ by a little; the method, not your arithmetic, is the reason.
What quartiles are for
Quartiles are the skeleton of the box plot and the input to the outlier rule: anything below Q1 − 1.5×IQR or above Q3 + 1.5×IQR gets flagged. They also power percentile-style reporting everywhere from growth charts ("your child is in the third quartile for height") to exam results.
Frequently asked questions
What is the difference between a quartile and a percentile?
They are the same idea at different resolutions. Q1 is the 25th percentile, the median is the 50th, and Q3 is the 75th.
Why does my quartile answer differ from my textbook?
Small datasets can be split several legitimate ways. This calculator uses the linear interpolation method (Excel QUARTILE.INC). Other methods (QUARTILE.EXC, Tukey hinges) can differ slightly on small samples; the answers converge as data grows.
What is Q2?
Q2 is the median: the 50th percentile, the middle value of the sorted dataset.