In statistics, the Freedman–Diaconis rule, named after David A. Freedman and Persi Diaconis, can be used to select the size of the bins to be used in a histogram. The general equation for the rule is:
where is the interquartile range of the data and is the number of observations in the sample
Another approach is to use Sturges' rule: use a bin so large that there are about non-empty bins (Scott, 2009). This works well for n under 200, but was found to be inaccurate for large n. For a discussion and an alternative approach, see Birgé and Rozenholc.