Morgan Stanley’s Katy Huberty believes Apple’s (AAPL) revenue most closely tracks how much it spends on new equipment (in MBA terms, CapEx ex-retail stores). Her chart looks like this:

By that formula, Apple’s revenues will hit $183 billion by the end of fiscal 2012.

Asymco‘s Horace Dediu has drilled a little deeper into Apple’s capital expenditures. He believes Apple’s sales of iOS devices (iPhones, iPads and iPod touches) most closely track Apple’s expenditures in machinery, equipment and real estate. His chart looks like this:

Dediu concludes that Apple’s projected $8 billion capital expenditures in 2012 means iOS device sales — the primary source of Apple’s revenue these days — will continue growing at the rate they always have: 100% per year.

On Wednesday, Seeking Alpha published an article by Bill Maurer — a recent college graduate taking advantage of the site’s open door policy — to offer a third theory. Rather than bemoaning the fact that Apple’s share price bears little relationship to its earnings (witness its shrinking price-to-earnings ratio), he suggests that the growth in Apple’s share price most closely tracks its revenue growth. He’s got a point. Over the past six years, Apple’s …

Earnings have grown 1852%
Sales have grown 677%
Share price has grown 660%

Maurer assumes (without explaining why) that Apple’s revenues will grow 28.5% in fiscal 2012 and 15% in fiscal 2013, and he concludes that Apple’s share price will hit $600 at the end of 2013. He didn’t provide charts, so we took the liberty of graphing his spreadsheets. They look like this:

The revenue-to-price relationship is bumpier than Maurer’s theory suggests, but it’s interesting nonetheless. Especially if you substitute Huberty’s or Dediu’s future growth estimates for his.