Ratio of IT to H/ware & S/ware support

Hi all,
My manager needs as soon as possible some detail information about the industry norms of the ratio of IT staff to equipment and application support. In other words, how many IT personell should a company hire based on the amount of computers hardware and software that is being supported. I know it somewhere out there, but don’t have the time to search, if you could tell me where to look, I’d appreciate it.

Thanks
Cliff