# Excel Histogram How does it calculate bin width

1. Feb 6, 2010

Hey people,

I am trying to write my own histogram making code since the Excel one sucks IMO. I am having some trouble thinking the whole bin 'width' thing through though.
I plan on using the formula

number of bins = k = 1.87(N - 1)0.40 + 1 ​

Then I was going to figure out the bin width as

$$\frac{[MAX(data ) - MIN(data )]}{k}$$​

This will get me in the ball park, but it will result in bin widths that are sloppy like 1.111 - 2.222 and the like. They should be sensible intervals like: 0 - 10, 10 - 20... etc or 0.10 - 0.12, 0.12 - 0.14...etc
Anyone care to brainstorm on me with this? I was thinking I could do some sort of test on the data set to determine what decimal place the bin width needs to go out to.

Hopefully someone can decipher what I am talking about here and wants to jump on board!

Last edited: Feb 6, 2010
2. Feb 10, 2010