  We investigate experimentally the statistics of the free volume inside
bidimensional granular packings, for two different kinds of grains and two
levels of compaction. With the aim to gain new insight into the statistical
description of granular media, we measure the free volume distribution in
clusters of increasing size. Our main result is that the logarithm of the free
volume distribution scales in a nonextensive way with the cluster size, while
still enabling the extraction of two intensive parameters. We discuss the
interpretation of these parameters, and the consequences of the nonextensivity
on the possible measurements of Edwards' ''compactivity''.
