How to Calculate Quartile
What is Quartile?
Quartiles divide a sorted dataset into four equal parts. Q1 (25th percentile) is the median of the lower half, Q2 is the overall median, Q3 (75th percentile) is the median of the upper half. The IQR (Q3−Q1) measures the middle 50% spread.
Step-by-Step Guide
- 1Sort data in ascending order
- 2Q2 = median of all data
- 3Q1 = median of lower half (below Q2)
- 4Q3 = median of upper half (above Q2)
- 5IQR = Q3 − Q1; Outlier if < Q1 − 1.5×IQR or > Q3 + 1.5×IQR
Worked Examples
Input
1, 2, 3, 4, 5, 6, 7, 8
Result
Q1=2.5, Q2=4.5, Q3=6.5, IQR=4
Input
10, 20, 30, 40, 50, 100
Result
Q1=20, Q2=35, Q3=50, IQR=30
100 is an outlier: > Q3+1.5×30 = 95
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