tinqlam:
Are you referring to a home that you will use for a residence? Or a home that will be used for rental?
If this is for a residence, MikeOH stated you may use market sales comps to determine a value; you may also pay for an appraisal, or get a real estate agent's opinion.
If this is a rental, you may use the previously stated formula.
However, if you are wondering whether there is a 'standard' cap rate for single family home rentals, I don't know if there is any nationwide average, like one can find for apartment buildings.
(If anyone knows of such a resource for SFHs, please post it!)
For my potential rental homes, the cap rate I want will differ from property to property, depending upon such factors as management headaches, location, appreciation potential, anticipated maintenance costs, etc.
Then, to help keep me grounded, I compare that rate with what I can get from CDs, or a nice broad market mutual fund.
Plugging numbers into a formula is the easy part. The beauty, and danger, of real estate investment lies in the fact that it is as much 'art' as it is 'science'.