Class Width Calculator
Determine the class width for grouped frequency tables or histograms by supplying the data range and target number of classes.
Raw class width
9.375
Rounded class width
10.000
Rounded to the nearest 1
How to Use This Calculator
- Enter minimum and maximum values for your dataset.
- Choose the desired number of classes (k).
- Optionally specify a rounding increment for a tidy class width.
- Use the rounded width to build class intervals for histograms or frequency tables.
Formula
Class width = (Max − Min) / Number of classes
Round the result to a convenient number (e.g., nearest 1, 5, or 10) to form readable class boundaries.
Frequently Asked Questions
How many classes should I use?
Sturges’ rule (k ≈ 1 + 3.3 log₁₀ n) or the square-root rule (k ≈ √n) are common starting points.
Can class widths be unequal?
Yes, but equal widths simplify interpretation. Unequal widths require density adjustments in histograms.
Should interval endpoints overlap?
Use half-open intervals (e.g., [10, 20), [20, 30)) to ensure each observation fits exactly one class.