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SESK: Stuff Everyone Should Know · sesk.info/aero-chart-obstacle-agl

Next to a tower on a sectional chart, what does the number in parentheses show?

The tower's height above the ground (AGL).

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  1. Its height above the ground ✔
  2. Its height above sea level
  3. Its radio frequency

Why: Obstacles show two numbers. The top one is the height of the tower's top above sea level (MSL). The number in parentheses below is how tall it is above the ground (AGL).

Huh, didn't know that: In very crowded areas the FAA may leave off the AGL numbers to keep the chart readable.

The dad joke
Why did the tower wear parentheses? It wanted to keep its height in brackets.
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References

Answer: Its height above the ground. Obstacles show two numbers. The top one is the height of the tower's top above sea level (MSL). The number in parentheses below is how tall it is above the ground (AGL).

  1. FAA Aeronautical Chart Users' Guide (VFR Sectional Charts) aeronav.faa.gov/user_guide/cug-complete_20260709.pdf
    The AGL height is in parentheses below the MSL elevation.
    Checked 2026-10-10.

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