Enter either the operating frequency or the loop circumference (total wire length) into the calculator to estimate the other value. This calculator uses the speed of light (c = 299,792,458 m/s) and a typical trim factor of k = 0.95 as a starting point for a resonant full-wave loop; final dimensions should be trimmed/tuned for your specific build and environment.

Antenna Loop Calculator

Enter either Frequency or Loop Circumference to calculate the other (leave one field blank).

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Full-Wave Loop Antenna Length Formula

The following formula is used to estimate the circumference (total wire length) of a resonant full-wave loop for a given frequency (starting point before trimming/tuning).

L \approx \frac{c}{f}\times k

Variables:

  • L is the loop circumference (total conductor length) in meters (m)
  • c is the speed of light (exactly 299,792,458 meters per second)
  • f is the frequency in hertz (Hz)
  • k is a trim factor (often started around 0.95 for typical wire loops; final value depends on wire/insulation, height, nearby objects, and is tuned in practice)

To estimate the loop circumference, first compute the free-space wavelength (c / f), then multiply by a trim factor (k). Note that “loop antennas” also include small loops with circumference much less than a wavelength; the formula above is intended for resonant full-wave loops, not small-loop designs.

What is an Antenna Loop?

An antenna loop, also known as a loop antenna, is a type of radio antenna that consists of a loop or coil of wire, tubing, or other electrical conductor. Loop antennas range from small loops (with circumference much smaller than a wavelength, often used for receiving and direction finding) to resonant loops (with circumference on the order of one wavelength, often used for HF transmitting/receiving). The loop works by receiving and transmitting signals through electromagnetic fields created by current flowing through the conductor, and its radiation pattern depends on the loop’s shape and orientation. Loop antennas are commonly used in applications such as AM reception, shortwave listening, and two-way radio communication systems.

How to Calculate Antenna Loop?

The following steps outline how to estimate a resonant full-wave loop circumference from frequency.

  1. Determine the operating frequency (f).
  2. Convert the frequency to hertz (Hz) if needed.
  3. Calculate the free-space wavelength: λ = c / f.
  4. Estimate the loop circumference (total wire length): L ≈ λ × k (a common starting point is k ≈ 0.95, then trim/tune as needed).
  5. Optionally, for a square loop, each side length is approximately L / 4. Check your result with the calculator above.

Example Problem : 

Use the following values as an example problem to test your knowledge.

Frequency (f) = 14.2 MHz

Using k = 0.95, the estimated loop circumference is L ≈ (299,792,458 / 14,200,000) × 0.95 ≈ 20.06 m (≈ 65.80 ft).