There are 50 values in the data set, the smallest is 38.13 and the largest 62.58

Using the square root rule suggests about 7 bins with a bin width of:

I'll make the first bin extend from 36.75 to 40.25; this will give a midpoint of 38.5 and subsequent bins will either be whole numbers or end with '.5'. I created a table in Excel:

Pass your mouse over the image to see the frequency table created by Excel.


The number of bins given by the formula is a guide, and you can vary it to suit your preferences. Sometimes a different set of bin values will work better.

I like 'nice' bin sizes and also think that the square root rule usually gives fewer bins than I like, so I adjust the number of bins upwards until I get a bin size I like. In this case I would go for a bin size of 2.5 because it is a 'simple fraction' of ten.

Pass your mouse over the image to see the histogram with a bin size of 2.5