Typically, the GRM is the "Product" of Price / Gross Annual Rent. Ie 10x gross = $50,000 (gross rent) = $500,000.
Cap rate is a little more complicated but is typically also a product of Net operating income and Price. If you know Cap and know income then you can also solve ie $25,000 net income / 6% = $416,000.
You can solve for any item in an equation. However, you will be manipulating rental numbers and they should be estimated at a realistic range.
Oct 3, 2013