Struggling with Histogram Bin Width and Bin Intervals?
QI Macros addin for Excel can calculate these for you!
Draw a Histogram using QI Macros
 Select your data.
 Select Histogram on QI Macros menu.
 QI Macros will do the math and draw the graph for you.
Go Deeper: Here's How to Calculate the Number of Bins and the Bin Width for a Histogram
 Count the number of data points.
 Calculate the number of bins by taking the square root of the number of data points and round up.
 Calculate the bin width by dividing the specification tolerance or range (USLLSL or MaxMin value) by the # of bins.
Bin Width = (MaxMin)/sqrt(n)
Histograms Can be Painfully Hard to Create
To create a histogram manually or using Excel,
you will need to calculate:
the number of bins bin width bin intervals.
The many steps are described below.
...or you can use QI Macros addin for Excel.
It calculates the bins and widths automatically
and draws the chart.
Download a free 30 day trial and
you'll have a histogram in minutes.
Example of Calculating Bins and Bin Width
Description 
Example of Calculation In Excel 

Step 1: Count the Number of Data Points Let's say we have 50 data points. If your data is in Excel, use Excel's count function to determine the number of data points. 

Step 2: Calculate the # of Bins, then round up # of bins = square root of the # of data points the square root of 50 = 7.071, round up to 8 In Excel, add the SQRT function to your calculation then add the Roundup function. 

Step 3: Calculate the Bin Width Bin width = Spec Tolerance or Range ÷ number of bins
If we use the range for this example: Bin width = (MaxMin) ÷ Number of bins Bin width = (346  187) ÷ 8 = 19.875

Now Create a Histogram in Excel Using These Bin Widths
Bin intervals need to span enough distance to include the upper and lower spec limits and the min and max values. Using the data in the previous example, follow these steps to determine bin intervals for a histogram:
 select a beginning point that is lower than or equal to both the lower spec limit and the min value
 calculate bin intervals in Excel by taking the beginning value + the bin width, + the bin width, etc.
 round the calculated values if desired
 select an ending point that is higher than or equal to both the upper spec limit and the max value
Note: Upper and lower specification limits are determined by the customer of the process. If you don't have spec limits, use the maximum and minimum values.
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Juran's Guidelines for 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  Number of Data Points  Number of Bars  
2050  6  201500  9  
51100  7  5011000  10  
101200  8  1000+  1120 
Stop Struggling with Histograms
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