Show HN: Free box plot maker with CSV upload and automatic outlier detection

1. Enter Your Data

Type or paste your numbers into the input box. You can use commas, spaces, or line breaks to separate values. Alternatively, upload a CSV file or paste data directly from Excel or Google Sheets.

2. View Instant Results

Our box plot generator automatically calculates quartiles, detects outliers, and generates your box plot in real-time. The five-number summary displays below the chart with detailed statistics including Q1, median, Q3, and IQR.

3. Export and Share

Download your box plot as a high-quality PNG image for presentations or export your data and statistics as CSV. No signup or installation required.

Understanding the Five-Number Summary

• 1

  Minimum: The smallest value in your dataset (excluding outliers)

• 2

  First Quartile (Q1): The value below which 25% of your data falls - also called the 25th percentile

• 3

  Median (Q2): The middle value that divides your data into two equal halves

• 4

  Third Quartile (Q3): The value below which 75% of your data falls - also called the 75th percentile

• 5

  Maximum: The largest value in your dataset (excluding outliers)

Box Plot Components Explained

• The Box (IQR): Represents the middle 50% of your data (from Q1 to Q3). The width of the box shows the interquartile range.
• Median Line: The line inside the box showing the median value. If it's not centered, your data is skewed.
• Whiskers: Extend from the box to show the range of the data, typically extending to 1.5 × IQR from the quartiles.
• Outliers: Individual points beyond the whiskers, representing unusual values that deserve investigation. Our box plot maker with outliers detection automatically identifies these for you.

Box Plot Maker vs Excel: Feature Comparison

While Excel can create box plots (version 2016+), our dedicated online box plot generator offers a more streamlined, user-friendly experience specifically designed for statistical visualization.

Best Use Cases for Box Plots

• 1

  Comparing Multiple Groups: When you need to compare test scores across different classrooms, sales performance across regions, or patient outcomes across treatment groups, box plots show the differences at a glance.

• 2

  Identifying Outliers: Box plots automatically highlight unusual values that fall outside the typical range. This is crucial in quality control, fraud detection, and scientific research where outliers may indicate errors or interesting phenomena.

• 3

  Checking Data Symmetry: The position of the median line within the box tells you if your data is symmetrical or skewed. This information is essential before choosing statistical tests.

• 4

  Large Datasets: When working with hundreds or thousands of data points, box plots summarize the distribution without overwhelming your audience with raw numbers.

Step-by-Step Interpretation

Education: Comparing Test Scores

A teacher analyzing exam scores across three classes (A, B, and C) uses box plots to compare performance. The visualization reveals that Class A has a higher median score (75) than Classes B and C (68 and 70), but also shows greater variability with more outliers. This insight helps the teacher identify both high achievers and students who need extra support.

Key Finding: The box plot immediately showed that while Class A's average was higher, Class B had more consistent performance with fewer struggling students.

Healthcare: Patient Recovery Times

A hospital compares recovery times for patients receiving three different treatment protocols. Using our free box plot generator, researchers visualize that Treatment A has a median recovery time of 7 days with a narrow IQR (5-9 days), while Treatment B shows 10 days with high variability (6-14 days). The box plots also reveal several outliers in Treatment C, prompting investigation into patient-specific factors.

Key Finding: Treatment A not only had faster median recovery but also more predictable outcomes, making it the preferred option for most patients.

Business: Sales Performance Analysis

A sales manager analyzes monthly revenue across four regional teams. The box plot reveals that the West region has the highest median sales ($125K) but also the most outliers, suggesting inconsistent performance. The East region shows lower median sales ($95K) but tight clustering, indicating reliable, steady performance. This visualization guides strategic decisions about team training and resource allocation.

Key Finding: The West region's outliers represented both exceptional wins and significant losses, prompting management to investigate what factors drove these extremes.

Environmental Science: Temperature Measurements

Climate researchers use box and whisker plots to compare daily temperature readings across different seasons. The box plots show that summer temperatures have a higher median (28°C) with relatively low variability (IQR of 4°C), while spring shows greater temperature fluctuations (IQR of 8°C) and several cold outliers below 10°C representing late frosts.

Key Finding: The visualization confirmed that spring is the most unpredictable season, with temperature outliers occurring far more frequently than in other seasons.

To make a box plot using our tool:

1. Enter your numbers in the input box separated by commas, spaces, or line breaks, or upload a CSV file
2. The tool automatically calculates quartiles and detects outliers
3. View your interactive box plot with the five-number summary
4. Download as PNG or CSV

No installation or signup required.

In Excel 2016+:

1. Select your data
2. Insert → Charts → Box and Whisker
3. Customize

However, our online box plot maker is easier: just paste Excel data directly, and get instant results with automatic outlier detection and better visualization options. You can also upload Excel files saved as CSV.

The five-number summary consists of:

1. Minimum
2. First Quartile (Q1 - 25th percentile)
3. Median (Q2 - 50th percentile)
4. Third Quartile (Q3 - 75th percentile)
5. Maximum

Our box plot calculator displays all these statistics automatically.