How to use the five-number summary calculator
- Copy your numbers from Excel or Google Sheets and paste them into the box, or type them separated by commas or spaces. They don't need to be in order.
- Keep the TI-84 / textbook quartile method unless your class uses Excel's QUARTILE.INC.
- Click Calculate summary.
- Read the minimum, Q1, median, Q3 and maximum, the IQR and any outliers, and check the labeled box plot.
- Follow the steps to see how each quartile was found, or open the data in the box plot maker for a downloadable chart.
How the five-number summary is calculated
Sort the data from smallest to largest, then:
- Minimum and maximum: the first and last values.
- Median: the middle value, or the average of the two middle values when n is even.
- Q1: the median of the lower half of the data; Q3: the median of the upper half. When n is odd, the overall median is left out of both halves (TI-84 method).
The spread of the middle half, and the fences that decide which values are outliers:
IQR = Q3 − Q1 , fences = Q1 − 1.5 × IQR and Q3 + 1.5 × IQR
- Q1
- The first quartile: 25% of the data are at or below it
- Median
- The second quartile: half the data are below it and half above
- Q3
- The third quartile: 75% of the data are at or below it
- IQR
- The interquartile range, the width of the middle 50% of the data
- Fences
- Values beyond 1.5 IQRs below Q1 or above Q3 are flagged as outliers
Worked example
Find the five-number summary of 8 quiz scores: 9, 4, 12, 5, 7, 4, 8, 2.
-
Sort them
2, 4, 4, 5, 7, 8, 9, 12
-
n = 8 is even, so the median is the average of the 4th and 5th values
Median = (5 + 7) / 2 = 6
-
Q1 is the median of the lower half (2, 4, 4, 5); Q3 of the upper half (7, 8, 9, 12)
Q1 = (4 + 4) / 2 = 4, Q3 = (8 + 9) / 2 = 8.5
-
The five-number summary
2, 4, 6, 8.5, 12
-
IQR and outlier fences
IQR = 8.5 − 4 = 4.5; fences: 4 − 6.75 = −2.75 and 8.5 + 6.75 = 15.25
What it means: half the scores are between 4 and 8.5, the typical score is 6, and since every value is inside the fences there are no outliers. Excel's QUARTILE.INC would give Q3 = 8.25 instead of 8.5, a small difference from the method.
How to interpret the five-number summary
- Center: the median is the typical value, and isn't pulled by extreme values the way the mean is.
- Spread: the IQR is the width of the middle half of the data. A bigger IQR means more variation.
- Shape: if the median is closer to Q1 than to Q3, and the maximum is far out, the data are skewed right. The opposite pattern means skewed left.
- Outliers: values beyond the fences deserve a second look: a typing error, or a genuinely unusual case.
The box plot maker draws the summary for one or more groups side by side, and the guide to reading a box plot explains each part.