diff --git a/file_utils/README b/file_utils/README
index 897d1e4..6ab0399 100644
--- a/file_utils/README
+++ b/file_utils/README
@@ -14,6 +14,11 @@ separated on several archives, they will be on the same volume.
 Note: I kept the datapacker's terminology in which a volume is also
 called a bin.
 
+The default bin size is 703 MiB, i.e. the capacity of a 80-minute
+CD-ROM; note that this can lead to slightly exceed the capacity when
+actually burning the disc, so if you don't want to overburn a few
+hundreds KiB, choose a lower bin size (702 MiB should be fine).
+
 By default, dirpacker displays a list of bins and the files they
 would contain, along with the size of each file and some statistics.
 With the option --machine-readable, this list will be printed in a