as usual the Rob is right. -v shows load factor:
$ ischk
ischk ------- PRO-IV (R) Verify internal structure of PRO-ISAM files
Copyright (C) 1999 PROIV Technology, Inc.
All rights reserved. Unauthorised use strictly prohibited.
PRO-ISAM Version: 13.04.15.01S Date: Mar 17, 2000
usage: ischk {-s} {-nyv} filename(s)
options;
-s Suppress the Copyright banner.
-n Automatically answer N(o) to 'Repair File'
-y Automatically answer Y(es) to 'Repair File'
-v Verbose mode. Report page allocation and load factor
filename(s);
One or more PRO-ISAM files seperated by spaces.