Softonic

Quartile Calculator

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Quartiles split an ordered dataset into four equal parts. This calculator sorts your values, then reports Q1 (25th percentile), the median (Q2), Q3 (75th percentile) and the interquartile range so you can describe the middle 50% of your data without opening a stats package.

How to compute quartiles

  1. 1

    Paste your dataset

    Enter numbers separated by commas, spaces, semicolons or line breaks. Use a full stop as the decimal mark; non-numeric tokens are ignored.

  2. 2

    Sort happens automatically

    The calculator sorts the values ascending before computing percentiles.

  3. 3

    Read the five-number summary

    You will see count, min, Q1, median, Q3, max and IQR = Q3 - Q1.

  4. 4

    Use IQR to spot outliers

    Values below Q1 - 1.5 x IQR or above Q3 + 1.5 x IQR are classic Tukey outliers.

Linear interpolation method

This tool uses the linear-interpolation percentile definition (the same one NumPy calls linear and Excel calls PERCENTILE.INC). For a sorted sample of n values, the rank of the p-th percentile is (p / 100) * (n - 1). If that rank is not a whole number the result is interpolated between the two neighbouring values.

How definitions compare

Method Known as Behaviour on small samples
Linear (this tool) Excel INC, NumPy linear Smooth, matches most stats courses
Exclusive Excel EXC Undefined for the very tails
Tukey hinges A boxplot convention Can give different Q1/Q3 on small samples

Reading the IQR

  • A small IQR relative to the range signals a tight cluster with long tails.
  • A large IQR suggests a wide spread in the middle of the distribution.
  • A quick outlier fence: [Q1 - 1.5 * IQR, Q3 + 1.5 * IQR]. Points outside are worth inspecting.

Frequently Asked Questions

Excel has two functions: PERCENTILE.INC (linear, same as this tool) and PERCENTILE.EXC (exclusive). If you used EXC, tail quartiles will differ: especially on datasets with fewer than ten points.

Yes. Sign is preserved during sorting, so negative values sit at the bottom of the ordered list and feed into Q1 just like any positive value.

Yes. Line breaks, tabs, spaces, commas and semicolons all work as separators, so a column from Google Sheets or Excel will parse as-is.

Duplicates are kept. They count towards the sample size and shift the percentile ranks: this is the correct behaviour for empirical quartiles.

Yes. The numbers are sent to our server to calculate the result, and the step-by-step mode can also place them in the URL. Do not enter sensitive data.

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