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Outlier finder

Find unusually high or low values in every number column. Free, private and browser-based.

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Free workspace supports five open files. Each file can be up to 100 MB.

About the Outlier finder

Open a CSV or Excel file and every number column is checked for values far from the rest — a price typed with an extra zero, a reading in the wrong unit, or a genuinely unusual case worth a look. Each outlier is listed with its row, whether it is too high or too low, and how far out it is.

How to use it

  1. Open or drop a CSV, XLS or XLSX file.
  2. Choose the rule: the IQR rule (the usual choice), extreme values only, or z-scores.
  3. Check the rows listed for each column, and download them as CSV.

Tip: The IQR rule is the safer default: a few huge values make the standard deviation bigger, which can hide other outliers from a z-score test.

Questions

What is the IQR rule?

IQR is the spread of the middle half of the values (the third quartile minus the first). A value more than 1.5 IQRs below the first quartile or above the third is an outlier; more than 3 IQRs is an extreme one. It is the rule a box plot uses.

Should I delete outliers?

Not automatically. Check each one: fix typos and unit mistakes, and keep real values — they are often the most interesting rows.

How are numbers like 1,234.50 or 12% read?

As spreadsheets show them: thousands separators, decimal commas, percentages, currency signs and (3) for minus 3 are all understood.

Is my data uploaded?

No. The tool runs in your browser; what you paste or open never leaves your device and nothing is stored on a server.