Outlier Calculator

About this tool

What Is the interquartile range method? Outlier Calculator. The outlier calculator scans a dataset for extreme values using Tukey's fences: values below Q1 − 1.5·IQR or above Q3 + 1.5·IQR are mild outliers, and values beyond 3·IQR fences qualify as extreme. The IQR method measures spread by the middle 50% of the data: IQR = Q3 − Q1. Multiplied by 1.5 and placed around the quartiles it forms fences that flag genuine extremes instead of ordinary variation. The tool reports the five-number summary, the fences, and every flagged value with its severity, so the decision is transparent rather than a black-box verdict. IQR = Q3 − Q1; fences = Q1 − 1.5·IQR and Q3 + 1.5·IQR. How to Use Enter your dataset as numbers separated by commas, spaces, or one per field. Read the sorted values, quartiles, and IQR. See each flagged outlier under the 1.5 and 3.0 fence rules. Worked Example With the list 10, 12, 13, 14, 18, 42 the tool computes Q1 = 12, Q3 = 18, IQR = 6, so the upper fence is 18 + 1.5·6 = 27; 42 lies beyond both 27 and 36, so it is flagged as an extreme outlier. Common Use Cases data cleaning before analysis sensor reading sanity checks grade-curve reviews for anomalies fraud-ish spikes in financial logs Important Notes The 1.5 fence marks mild outliers; 3.0 marks extreme ones. Quartiles use the standard exclusive median splitting method. Processing happens entirely in the browser.