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Not Sure How to Calculate the # of Bars for a Histogram?

QI Macros add-in for Excel can calculate these for you!

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Go Deeper: Here's How to Calculate the Number of Bars Manually

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 to Minitab® and you'll see they are similar:

Other Histogram Information

• Create a histogram in Excel using QI Macros
• Cp, Cpk and other process capability formulas
• Capability suite of six charts

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

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