TV Fool is a service that allows you to input your address (or GPS coordinates) and see what OTA TV stations you will receive. To find Latitude and Longitude coordinates you can go to http://www.latlong.net/
After you enter in a address you will get a image like this back. When trying to decipher the image you get back from the website, there will be an additional chart to help.
It says that “Green” an indoor “set-top” antenna is probably sufficient to pick up these channels. “Yellow” is an attic mounted antenna is probably needed to pick up channels at this level and above. “Red” is a roof-mounted antenna is probably needed to pick up channels at this level and above. “Grey” These channels are very weak and will most likely require extreme measures to try and pick them up.
To make life a little easier (or a hint) you can click on the transmitters (On the top right of the picture) to see terrain obstacles and how those obstacles combined with transmitter strength will affect your reception of channels.
Under NM (Signal) is the expected noise margin of each channel “in the air” at your location, specified in dB. You must add/subtract any gains/losses you get from your antenna, building penetration, amps, cables, splitters, and other factors present. Ideally, the detection threshold (NM value) above 0 will pick up a station. So if you look at the report assigned to my moms house, you would notice that she should (might) get 12 stations. (Tip: There have been studies that have shown an amplifier used when close to towers actually hurts your reception more than it helps) I just wanted to point out. That the same report with an antenna height at 10 (as opposed to 5) has 20 stations with a NM value over 0, so height makes a big difference.