Histogram Number of Bars

One of the most frequent questions we get is: "How do you select the number of bars on the histogram?"

The simple answer is we round the square root of the number of data points. For example:

  • 25 data points = 5 bars
  • 100 data points = 10 bars

If there are too many bars (e.g., more than 50) to display nicely on the page, we limit the number of bars.

Juran's Quality Control Handbook provides these guidelines for the number of bars and states that they are not "rigid" and should be adjusted when necessary.

    Number of Data Points Number of Bars

    20-50

    6

    51-100 7
    101-200 8
    201-500 9
    501-1000 10
    1000+ 11-20

QI Macros prompts you for the number of bars you would like, however, you won't always get exactly the number you input. Why? Because we're trying to fit the graph to the page between varying specification limits within the constraints of Excel while still making it as readable as possible.

Compare QI Macros histograms Minitab® and you'll see they are similar:

QI Macros histogram in excel


QI Macros histogram with normal curve in excel
QI Macros histogram example skewed to the left
QI Macros histogram in excel

Other Histogram Information

Process Capability Analysis Quick Reference Card

Download a FREE PDF of histogram formulas and sample calculations

The histogram is just one of the tools included in the QI Macros for Excel SPC Software for Excel.


Why Choose QI Macros to Perform Capability Analysis and Draw Histograms?

affordable

Affordable

  • Only $279 USD - less with quantity discounts
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  • Free Technical Support

easy to use

Easy to Use

  • Works Right in Excel
  • Calculates Cp Cpk Pp Ppk
  • Accurate Results Without Worry

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