Fresnel Zone Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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A fast fresnel zone estimate is valuable only when the setup is clear. Many E&M relationships are simple proportionalities or inverse powers, making a one-input sensitivity check an effective way to catch unit mistakes. The sections below show exactly what this page calculates, how to enter the data, and where the simplified model stops.

What this calculator does

The calculator isolates the relationship between Frequency, Distance between the antennas (D), Distance from the emitter antenna (d₁) and first Fresnel-zone radius. That makes it useful for testing how one input changes the answer without mixing in unrelated assumptions.

How to use it

Fill in Frequency, Distance between the antennas (D), Distance from the emitter antenna (d₁), Distance from the receiver antenna (d₂) exactly as defined on the page. After calculating, change one influential input slightly and confirm that the result moves in the direction predicted by the equation; this is a quick unit and setup check.

How the calculation works

For wavelength λ = c/f, the first-zone radius at a point is r1 = √[λd1d2/(d1+d2)]. At the midpoint of a link of total length D, the largest first-zone radius is ½√(λD).

Example

At 2.4 GHz, wavelength is about 0.125 m. For a 10 km link, the largest first Fresnel-zone radius at the midpoint is about 17.7 m. The current page can reproduce this radius when frequency and total distance are entered; it does not use antenna height to calculate clearance.

How to interpret the result

Use the first Fresnel-zone radius as the result of the stated electromagnetic relationship. Check whether the output is linear, inverse, inverse-square, or logarithmic before judging how a change in one input should affect it.

Limitations and notes

Several visible fields are not active in the current output: the Calculate selector does not invert the formula for frequency, and antenna/obstruction heights are not used for clearance. The page calculates radius only when frequency plus total distance or the two segment distances are entered.