About this calculator
The calculator flags outliers using Tukey’s rule: anything more than 1.5 × IQR below Q1 or above Q3.
How to use it
- Enter the numbers.
- Choose the quartile method.
- Read the IQR and outliers.
The formula
IQR = Q3 − Q1; fences = Q1 − 1.5 × IQR and Q3 + 1.5 × IQR
- Q1, Q3
- first and third quartiles
Worked example
12, 14, 15, 15, 16, 18, 19, 21, 22, 45
- Q1 = 14.75 and Q3 = 21.25, so IQR = 6.5.
- Fences are 5 and 31; 45 is an outlier.
What the result means
An outlier is a value worth checking, not one to delete automatically. It may be a typing error or a genuine extreme.
Assumptions
- At least 3 numbers.
Limitations
- The fences depend on the quartile method chosen.
Frequently asked questions
What is a good IQR?
There is no good or bad value; compare it with the median or with other groups.
What is the 1.5 IQR rule?
Values more than 1.5 × IQR beyond the quartiles are called outliers.
What is quartile deviation?
IQR ÷ 2, also called the semi-interquartile range.
Last reviewed on 6 October 2026. Found a mistake? Tell us.