  The design of software development tools follows from what the developers of
such tools believe is true about software development. A key aspect of such
beliefs is the size of code contributions (commits) to a software project. In
this paper, we show that what tool developers think is true about the size of
code contributions is different by more than an order of magnitude from
reality. We present this reality, called the commit size distribution, for a
large sample of open source and selected closed source projects. We suggest
that these new empirical insights will help improve software development tools
by aligning underlying design assumptions closer with reality.
