Outlier Detection Calculator
The outlier detector applies Tukey’s 1.5 × interquartile-range rule to flag unusually low or high observations for review.
How to use this calculator
- Enter at least four numerical observations. Review Q1, Q3, the fences and each flagged value together.
- Check the labels and units before using a result outside this page.
- Change one input at a time if you want to compare scenarios.
Formula and method
IQR = Q₃ − Q₁; lower fence = Q₁ − 1.5IQR; upper fence = Q₃ + 1.5IQR
- IQR = Q₃ − Q₁; lower fence = Q₁ − 1.5IQR; upper fence = Q₃ + 1.5IQR
- A statistical flag is not proof of an error; some genuine data are extreme and should not be removed without context.
Worked examples
Worked example
For 10, 11, 12, 13, 100, the unusually high value may fall above the upper fence depending on the quartile convention.
Sort the values, compute the lower and upper quartiles, then compare each observation with both fences.
Sort the values, compute the lower and upper quartiles, then compare each observation with both fences.
Understanding the result
The outlier detector applies Tukey’s 1.5 × interquartile-range rule to flag unusually low or high observations for review.
A statistical flag is not proof of an error; some genuine data are extreme and should not be removed without context.
Important notes
A statistical flag is not proof of an error; some genuine data are extreme and should not be removed without context.
Displayed outputs are rounded for readability; preserve full precision when continuing a calculation.
Frequently asked questions
What does this outlier detection calculator show?
The outlier detector applies Tukey’s 1.5 × interquartile-range rule to flag unusually low or high observations for review.
Which inputs should I check first?
Enter at least four numerical observations. Review Q1, Q3, the fences and each flagged value together.
Can the result be used as a final professional specification?
A statistical flag is not proof of an error; some genuine data are extreme and should not be removed without context.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.