Fresnel Zone Calculator
First Fresnel-zone radius at the midpoint and at any obstacle along a link — with the 60 % clearance rule applied.
Line of SIGHT is not line of LINK: a ridge or treetop poking into the lower 40 % of the first Fresnel zone can cost 6–20 dB even though you can “see” the far antenna. Lower frequencies need dramatically more clearance (the zone is √λ wider). Add Earth-curvature height on links beyond ~10 km.
Fresnel Zone Calculator computes the first Fresnel-zone radius along a wireless link and the clearance you must keep — free, instant and private in your browser. WISP installers, point-to-point WiFi builders and rural-link planners use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Fresnel Zone Calculator
Fresnel Zone Calculator computes the first Fresnel-zone radius along a wireless link and the clearance you must keep using the standard engineering relation: r = √(λ·d1·d2/(d1+d2)); midpoint shortcut r(m) = 8.66·√(D_km/f_GHz); keep 60 % clear. Worked live: an 8 km, 5.8 GHz link needs ~10 m of midpoint radius — 6 m of it must be obstacle-free. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Fresnel Zone Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Fresnel Zone Calculator?
- ✓Implements the real formula — r = √(λ·d1·d2/(d1+d2)) — with the substitution shown, not a black box
- ✓Built for WISP installers, point-to-point WiFi builders and rural-link planners
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate fresnel zone?+
The first Fresnel-zone radius along a wireless link and the clearance you must keep follows r = √(λ·d1·d2/(d1+d2)); midpoint shortcut r(m) = 8.66·√(D_km/f_GHz); keep 60 % clear. For example, an 8 km, 5.8 GHz link needs ~10 m of midpoint radius — 6 m of it must be obstacle-free. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
I can see the other antenna — why is my link still slow?+
Visual line-of-sight is a pencil; the radio needs a rugby-ball-shaped volume. A treetop or ridge intruding into the lower 40 % of the first Fresnel zone diffracts and cancels signal, costing 6–20 dB while looking 'clear' to the eye. Raise the antennas.
Do lower frequencies need more or less clearance?+
More: the zone radius grows with √λ. A 900 MHz link needs ~2.5× the clearance of 5.8 GHz over the same path — counterintuitive since low frequencies 'penetrate better'. They diffract better around obstacles, but want fatter clear zones when unobstructed.
Is the Fresnel Zone Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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