Loona Box Plot Maker — Free Box & Whisker Charts
Averages hide the spread. A box plot shows the median, where the middle half of values sits, and how far the extremes reach — the honest way to compare groups.
How to use the Box Plot Maker
- Enter each group’s raw values as one series — one value per row (rows are just slots; add more rows for bigger groups).
- The maker computes quartiles per series and draws one box per group.
- Compare medians and spreads, then download the PNG.
How it works
Quartiles use linear interpolation on the sorted values (the standard type-7 method used by spreadsheets). The box spans Q1 to Q3, the line inside is the median, and whiskers reach the minimum and maximum. The chart is drawn by hand on an HTML canvas by Loona’s shared chart engine — no chart library and no server. Everything is computed locally, so your numbers never leave your device.
Worked example
Two classes took the same test. Class A’s median is higher, but its box is wider — the plot shows both the win and the inconsistency in one picture.
Frequently Asked Questions
What do the box parts mean?
The box covers the middle 50% of values (Q1 to Q3). The line inside is the median. Whiskers reach the smallest and largest values.
How are quartiles calculated?
By linear interpolation on the sorted data — the same method as spreadsheet QUARTILE functions.
How many values per group?
At least four for a meaningful box; eight or more is better. All groups should have the same number of rows — pad a shorter group by repeating its median only if you understand the effect; better, collect equal samples.
Is my data private?
Yes — computed entirely in your browser.