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Upper and Lower Fence Calculator
Calculate the upper and lower fences used to flag outliers in a data set, based on the first and third quartiles (Q1 and Q3).
What are upper and lower fences?
Upper and lower fences are boundary values used to identify potential outliers in a data set based on the interquartile range (IQR). Data points falling outside the fences are typically flagged as unusually high or low.
The formula
IQR = Q3 − Q1. Lower Fence = Q1 − k × IQR. Upper Fence = Q3 + k × IQR, where k is commonly 1.5 for standard outlier detection or 3.0 for identifying only extreme outliers (this is the same method used to define the whiskers on a box plot).
This calculator is for general statistics education and exploratory data analysis purposes.
Last reviewed August 2026