Fresnel Zone Calculator — Radio Link Clearance
Enter the carrier frequency, total link distance and the zone number to find the Fresnel zone radius at the path midpoint — the clearance you must maintain above obstacles for optimal wireless link performance.
Frequency unit
km
Maximum radius of the nth Fresnel ellipsoid at the path midpoint
- 1
Wavelength λ = c / f
299 792 458 ÷ 2.4 GHz = 12.4914 cmWavelength in free space from the carrier frequency. - 2
Midpoint half-distance (d₁ = d₂)
5 km ÷ 2 = 2,500 mAt the midpoint d₁ = d₂ = total distance / 2, giving the largest zone radius. - 3
Fresnel zone radius (n = 1)
√(1 × 0.124914 × 2,500 × 2,500 ÷ 5,000) = 12.50
How does this calculator work?
The nth Fresnel zone radius at the path midpoint is r_n = √(n·λ·d/4), where λ = c/f. For Wi-Fi or microwave links, keep at least 60% of the first Fresnel zone clear of obstacles to avoid diffraction loss. Enter frequency (MHz/GHz), total link distance (km) and zone number to get the clearance radius.
Formula
How this is calculated
Fresnel zones are a set of concentric ellipsoids around the straight line between a transmitter and a receiver. Radio waves travel not only along the direct path but also along slightly longer paths that reflect and diffract — if these contribute constructively they reinforce the signal; if they are blocked the signal degrades. The first Fresnel zone contains the most energy-carrying paths, so it is the most critical to keep free of obstacles.
The radius of the nth Fresnel zone at any point along the path is r_n = √(n · λ · d₁ · d₂ / (d₁ + d₂)), where d₁ and d₂ are the distances from the transmitter and receiver to that point and λ is the wavelength. The radius is largest at the midpoint of the path. This calculator evaluates the formula at the midpoint, which gives the maximum radius along the link and therefore the most conservative (safe) clearance estimate.
For practical link design, 60% clearance of the first Fresnel zone is the minimum recommended for acceptable performance; full clearance of the first zone (100%) is the engineering target. Obstructions inside 40% of the first zone cause measurable diffraction loss. Higher frequencies (GHz) produce smaller Fresnel zones and are easier to clear, which is why short microwave links often work despite modest antenna heights.
Frequently asked questions
The first Fresnel zone carries the majority of signal energy. Any obstruction inside it causes diffraction loss that reduces received signal strength. At 60% clearance the loss is negligible; at 100% you achieve free-space path loss performance.
Yes. Select GHz and enter 2.4 or 5.0, then enter the distance. For a 2.4 GHz link over 100 m the first Fresnel zone radius at the midpoint is about 1.8 m — so antennas should be at least 1.8 m above any obstacle along the path.
At any point where the distance from the transmitter is d₁ and from the receiver is d₂ (with d₁ + d₂ = total distance d), the radius is r_n = √(n · λ · d₁ · d₂ / (d₁ + d₂)). The midpoint (d₁ = d₂) gives the maximum radius and is the standard design reference.
Also known as
TG we-Calculate Editorial Team. (2026). Fresnel Zone Calculator — Radio Link Clearance [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/fresnel-zone-calculator
TG we-Calculate Editorial Team. "Fresnel Zone Calculator — Radio Link Clearance." TG we-Calculate. 2026. https://we-calculate.com/calculator/fresnel-zone-calculator.
TG we-Calculate Editorial Team, "Fresnel Zone Calculator — Radio Link Clearance," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/fresnel-zone-calculator
@misc{wecalculate_fresnel_zone_calculator, title = {Fresnel Zone Calculator — Radio Link Clearance}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/fresnel-zone-calculator}}, year = {2026}, note = {TG we-Calculate} }
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