Ratio of Support Staff to Machines

I am the Technology Supervisor for a medium sized school district in NJ. I am responsible for purchasing, dealing w/vendors, contractors, salespersons – in addition to field support. I have 1 full time technician working for me and we are responsible for 6 buildings, each with its own LAN, each connected to a WAN, about 550 PC’s & servers – all networked, all w/Internet access.

I am pushing to hire a 2nd full time tech. – where can I find accurat data on realistic ratios of support personnel-to-PC’s, to validat my request to the Board of Education?