This calculator estimates the maximum radio line-of-sight distance between two antennas based on their heights above ground level. It assumes standard Earth curvature and no obstructions.

The formula used is: \[ \text{Distance (miles)} = 1.23 \times (\sqrt{h_1} + \sqrt{h_2}) \] \[ \text{Distance (km)} = 3.57 \times (\sqrt{h_1} + \sqrt{h_2}) \]

Where:

• h₁ = Height of antenna #1 (in feet)
• h₂ = Height of antenna #2 (optional, in feet)

You can leave the second height blank to calculate the line-of-sight to the radio horizon from just one antenna (e.g. a handheld or repeater tower).