Height Above Average Terrain Calculation

Height above average can be calculated by using an FCC government site if proper coordinates and antenna height are entered after conversion to meters.

  • Convert your elevation above sea level from feet to meters: feet above sea level divided by 3.281 = elevation ASL in meters.
  • Use the center of the antenna radiation for the height above ground, not the base.
  • Convert antenna height above ground level from feet to meters: antenna height above ground divided by 3.281 = height AGL in meters.
  • Add the ASL + AGL = antenna elevation above sea level in meters

    • Insert latitude, longitude and antenna elevation above sea level in meters (calculated above) into the HAAT Calculator

  • The program will give the HAAT of your antenna based on your entry data in meters.
  • Convert the HAAT from meters to feet: HAAT in meters times 3.281 = HAAT in feet. Put this on your TDS application.

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    Alternative Manual Calculation Using The Height Above Average Terrain Worksheet

    In the drawing below, the red dot is the transmitter. Each circle represents a distance of 2 miles further from the transmitter (2, 4, 6, 8 ,and 10 miles). The lines are at fixed points at 0, 45, 90, 135, 180, 225, 270, and 315 degrees. Add the ground elevations at each blue dot (where the degree lines and mileage circles intersect). Divide that number by 40 to get the average ground elevation.

    Now take the transmitter's elevation and add the height of the antenna above ground to it. Now subtract the average ground elevation from it. This is the height above average terrain.

    Note that this can be rather misleading. It can indicate that the antenna is actually at about 150 feet when it's really only 80 or 90 feet, also if the surrounding area is higher it can even be a negative number.

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