Radar Horizon Calculator
For radar and RF engineers, mariners and radio amateurs checking line-of-sight coverage before a link or watch — this tool applies the Bowditch horizon distances, 1.17√h visual and 1.22√h radar with h in feet, and adds both horizons when a target height is entered. The Bowditch distance to the horizon in nautical miles is 1.17×sqrt(h) visual and 1.22×sqrt(h) radar (where h is in feet); the range to a target adds both horizons.
0.0 nm
0.0 km
How to Use This Tool
- Choose ft or m from the unit dropdown — both height fields follow it.
- Enter the antenna (or eye) height above sea level.
- Optionally enter the target height; leave it blank for the antenna's own horizon.
- Pick Visual (1.17) or Radar (1.22) mode and read the total range in nm and km, with the substituted formula shown underneath.
FAQ
Q: What is the formula for radar horizon distance?
A: D(nm) = 1.22 × √(antenna height in feet); add √(target height in feet) inside the bracket for a target, and use 1.17 instead of 1.22 in visual mode — these are the Bowditch horizon distances.
Q: How far can a 100 ft radar antenna see?
A: 1.22 × √100 = 12.2 nm, about 22.6 km; adding a 25 ft target gives 1.22 × (10 + 5) = 18.3 nm, about 33.9 km, assuming a standard atmosphere.
Q: Do I have to convert metres to feet myself?
A: No — the unit dropdown converts each height to feet with 3.28084 ft/m before the formula runs, and the result is shown in both nautical miles and kilometres (1 nm = 1.852 km).
Q: Why are there two coefficients, 1.17 and 1.22?
A: 1.17√h gives the visual horizon and 1.22√h the radar horizon in nautical miles with h in feet; the tool applies whichever matches the mode you select and assumes a standard atmosphere.