David, generally speaking, you won't find any true "industry standard" for IT support, nor is it likely you will find any sort of automated tool to analyze your requirements. I did see a download for a spreadsheet to help determine IT support requirements on the TechRepublic home page today, but haven't had a chance to look at it.
Every environment and every group of users will be different. It is likely that an office full of users with Computer Science degrees will require a lot less support than an office of computer neophytes and techno-phobes. Common off-the-shelf software may require less intensive support than custom-built software. New computers are (usually) much less likely to break down, than computers that have been in use constantly for the last 10 years. Are your users such that you can show them how to do something once and they never bother you again? Or do you have users that you have to lead by the hand every time they need to move a document from one folderto another? Another key factor is the level of knowledge of your IT support staff.
You will obviously already know whether you are understaffed. But before you go on a hiring binge, there are a couple of things to consider. Start keeping statistics on help requests. Determine what are the most common help requests. Determine the average number of calls daily and sort by type of problem (how-to, hardware, software, etc.) Determine what is the average time to resolve a help request (factor in support staff expertise/competency). Determine what your average bag-log is and how this backlog affects user productivity (this may be somewhat objective). Determine if there are any common problems that could be better solved by user training vs. adding more support staff. Once you have all these statistics compiled, you will have a better idea on how to support your particular IT environment.
Good luck.