How to use the Quartile Calculator
- 1. Paste the dataEnter values in any order, separated by commas or spaces.
- 2. Pick a methodChoose the method your course, exam or software uses.
- 3. CompareSee all three methods in a table and the sorted data.
Three ways to find quartiles
Quartiles split sorted data into four equal parts, but there is no single agreed formula for small data sets:
- Inclusive (Excel QUARTILE.INC, NumPy): position (n − 1) × p from the first value, with interpolation.
- Exclusive (Excel QUARTILE.EXC): position (n + 1) × p.
- Median of halves (Tukey, many school textbooks): Q1 is the median of the lower half and Q3 the median of the upper half, leaving out the middle value when n is odd.
Worked example
Take 3, 7, 8, 5, 12, 14, 21, 13, 18. Sorted: 3, 5, 7, 8, 12, 13, 14, 18, 21, so n = 9 and the median is 12. Inclusive: Q1 sits at position 8 × 0.25 = 2, the third value, which is 7, and Q3 at position 6, which is 14. The result is Q1 7 · Q2 12 · Q3 14, with IQR 7. The exclusive method and median of halves both give Q1 = 6 and Q3 = 16, with IQR 10.
That difference is large on nine values and shrinks as data grows. Use whichever method your exam board or software expects, and say which you used. Python users: np.percentile(x, [25, 50, 75]) matches the inclusive row. The IQR feeds directly into outlier fences in the outlier detector and the box in the box plot maker. For other cut-offs such as the 90th percentile, use the percentile calculator.
Frequently asked questions
Which method does my calculator use?
Casio and TI calculators, and most Indian school textbooks, use the median of halves. Excel's older QUARTILE function equals QUARTILE.INC.
Is Q2 always the median?
Yes. All three methods give the same Q2, the ordinary median.
Is the Quartile Calculator free?
Yes, the Quartile Calculator is free. The first time you see your first result, you are asked for your name and WhatsApp number once. After that, this and every other Uncodemy tool opens straight away without the form.