Estimate the line-of-sight (LOS) distance to the horizon based on antenna height above ground level (AGL). The formula for geometric horizon distance is used. Also shown is the distance with a 15% addition which is the estimated amount that VHF and UHF can go beyond the horizon. This is based on the idea that VHF and UHF signals can travel beyond the geometric horizon due to atmospheric refraction.
The equation we can use to estimate this is roughly d = (1.23 * sqrt(h)) + (0.15 * (1.23 * sqrt(h))), where h is the height in feet and d is the distance in miles.