Fresnel Zone Calculator
How much clear space a point-to-point link needs around its line of sight. Enter the distance and frequency to see the first Fresnel zone and every step of the calculation.
How to use this tool controls and what to look for
Enter the length of a point-to-point link and its frequency, then move along the path to see how much clearance it needs.
Controls to change
- Distance: set the link length.
- Frequency: choose a band or enter a Custom frequency in MHz.
- Point along the path: move along the link to see the zone radius at any point. Midpoint jumps to the widest part.
What to look for
- The zone is widest in the middle and narrows to nothing at each antenna.
- Keep at least 60% of the first zone clear. Trees, roofs and the ground in the middle cause the most trouble.
- Longer links need much more clearance, and on links of a few kilometres the Earth's curvature adds to it.
- Higher frequencies give a thinner zone, so 5 GHz needs less clearance than 2.4 GHz over the same distance.
About this tool
The Fresnel zone is the rugby-ball-shaped space around the line of sight between two antennas that radio energy travels through. Obstacles inside it weaken the link even when the antennas can see each other. Enter the distance and frequency to see the first Fresnel zone, its radius along the path and every step of the calculation.
What you'll learn
- How to calculate the first Fresnel zone radius: r = 17.32 × √(d1 × d2 ÷ (f × D)), with distances in km and f in GHz
- Why at least 60% of the first zone should be kept clear
- How the zone grows with distance and shrinks at higher frequencies
- When the curvature of the Earth starts to matter
Common questions
How much clearance does a point-to-point link need?
Keep at least 60% of the first Fresnel zone clear. For a 1 km link at 5 GHz the zone's radius at the midpoint is about 3.8 m, so aim for about 2.3 m of clear space around the line of sight.
Why does a link fail with clear line of sight?
Trees, roofs or the ground inside the Fresnel zone cause diffraction and reflections that weaken or cancel the signal, even when the antennas can see each other.
Does a higher frequency need less clearance?
Yes. The zone gets thinner as frequency rises, so a 5 GHz link needs less clearance than a 2.4 GHz link over the same distance.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.