You will need the elevation for the site. This can be obtained through using Google Earth.
If the antenna is going on the roof of a building or on another structure (such as a water tower or tank) that has been registered with the FAA, enter the height of the building, tank or tower under "Supporting Structure Height" and the actual antenna (above the roof/top of the structure) under "Tower Height".
If the antenna is going on a free standing tower, leave the "Supporting Structure Height" value at 0 (zero) and enter the tower height (including the antenna height at the tip of the tower) in the "Tower height" field.
Click on "Compute" and the tool will look at each runway and determine if FAA notification may be required.
NOTICE: This tool is not intended to be a replacement for the FCC's TOWAIR tool but is intended to give a high level estimate of whether a location may be suitable for a new tower or antenna based on the location of airports in respect to the location of the tower. REC extends absolutely no warranty on this tool and those who depend on the data from this tool to make their final decision do so at their own risk.