About the Outlier Calculator
An outlier is a value that sits far away from the rest of the data. A common test is Tukey's rule: find the first and third quartiles, work out the interquartile range, and call anything beyond 1.5 times that range from the quartiles an outlier. This calculator does all of that for your list, shows the quartiles and the fences, and lists the values that fall outside them. Type your numbers and, optionally, the fence multiplier and the outliers appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Outlier Calculator
- 1Enter your numbers and, optionally, the fence multiplier.
- 2Pick the units or options from the menus if the outliers tool offers them.
- 3Read the outliers in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the outliers
Analysts use it to clean data before averaging, to spot typing errors, and to find unusual cases worth a closer look. In quality control it highlights faulty measurements. Box plots draw the same fences as whiskers.
An outlier is not always a mistake. It may be the most interesting value in the data. Check it before you delete it: look for a typing error, a different unit or a genuine rare event.
How the outliers is worked out
IQR = Q3 − Q1. Lower fence = Q1 − k × IQR. Upper fence = Q3 + k × IQR, with k = 1.5 normally (3 for extreme outliers). Quartiles use the same method as Excel's QUARTILE.INC. For 1, 2, 3, 4, 5, 6, 7, 8, 9 and 100, Q1 is 3.25 and Q3 is 7.75, so the IQR is 4.5 and the fences are −3.5 and 14.5. The value 100 lies above the upper fence and is an outlier. With k = 3 the upper fence would be 21.25, and 100 would still be flagged.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Adjustable multiplier
- Quartiles and fences shown
- Lists low and high outliers
Mistakes to avoid with outliers
Different programs compute quartiles in slightly different ways, so the fences can differ by a small amount from another tool's. This one uses linear interpolation. At least four values are needed. The rule works best for data that are roughly bell-shaped.
On phone and computer
On a phone, type into the boxes one after another and read the outliers underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the outliers move. The outlier calculator works the same on both. Finding an outlier means knowing where the middle of the data sits. See the quartiles with the Quartile Calculator, the spread with the Standard Deviation Calculator, and how far one value is from the mean with the Z-Score Calculator.
Features
- Check before removing
- Quartile methods differ
- k = 3 for extremes
- Clear messages when the outliers inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate outliers?
IQR = Q3 − Q1. Lower fence = Q1 − k × IQR. Upper fence = Q3 + k × IQR, with k = 1.5 normally (3 for extreme outliers). Quartiles use the same method as Excel's QUARTILE.INC. For 1, 2, 3, 4, 5, 6, 7, 8, 9 and 100, Q1 is 3.25 and Q3 is 7.75, so the IQR is 4.5 and the fences are −3.5 and 14.5. The value 100 lies above the upper fence and is an outlier. With k = 3 the upper fence would be 21.25, and 100 would still be flagged.
What is the formula for outliers?
IQR = Q3 − Q1. Lower fence = Q1 − k × IQR. Upper fence = Q3 + k × IQR, with k = 1.5 normally (3 for extreme outliers). Quartiles use the same method as Excel's QUARTILE.INC. The outlier calculator applies it exactly and rounds only the displayed answer to six significant figures.
Why 1.5 times the IQR?
John Tukey picked it as a practical cut-off that flags roughly 1 in 150 values in normal data.
What is an extreme outlier?
A value beyond 3 times the IQR from the quartiles.
Should I remove outliers?
Only if you can show they are errors. Otherwise keep them and report results with and without them.
Is this outlier calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.