Antenna Length Calculator
Enter a design frequency and antenna type to calculate element lengths in both imperial and metric units. Supports dipoles, verticals, end-fed half-waves, J-poles, ground planes, full-wave loops, and ⅝-wave verticals.
Common Band Center Frequencies — Quick Reference
| Band | Frequency |
|---|---|
| 160m | 1.9 MHz |
| 80m | 3.75 MHz |
| 60m | 5.357 MHz |
| 40m | 7.15 MHz |
| 30m | 10.125 MHz |
| 20m | 14.175 MHz |
| 17m | 18.118 MHz |
| 15m | 21.225 MHz |
| 12m | 24.94 MHz |
| 10m | 28.4 MHz |
| 6m | 52.0 MHz |
| 2m | 146.0 MHz |
| 1.25m | 223.5 MHz |
| 70cm | 440.0 MHz |
These are approximate center frequencies for the most popular amateur segments. Adjust to your specific operating preference (e.g. CW vs. SSB portions of HF bands).
Understanding Antenna Lengths
Why 468 and not 492? The theoretical half-wavelength in free space is 492 / fMHz feet. Real wire antennas are electrically shorter due to "end effects" — the capacitance at the tips of the wire slows the signal slightly. The empirical constant 468 (a shortening factor of approximately 0.952) accounts for this and produces a good starting point for a resonant half-wave antenna built with typical wire gauges (#12 – #14 AWG) at reasonable heights.
Velocity Factor (VF) describes how fast a radio signal travels through a conductor relative to the speed of light. Bare copper wire has a VF of roughly 0.95 (already built into the 468 constant). Insulated wire, coaxial cable stubs, and enclosed elements (like copper pipe J-poles) each have different velocity factors. If you're building with a non-standard material, entering the correct VF here will adjust all calculated lengths accordingly.
Always cut long and trim. These calculations are starting points. Real-world resonance depends on height above ground, nearby structures, wire gauge, feed-line interaction, and antenna shape. Cut your wire 2–3% longer than calculated, then use an antenna analyzer or SWR meter to trim to the desired resonant frequency.
Multi-band operation: End-Fed Half-Wave (EFHW) antennas cut for a fundamental frequency will also resonate on harmonic multiples — for example, an EFHW cut for 7.150 MHz (40 meters) also works on 14.3 MHz (20m), 21.45 MHz (15m), and 28.6 MHz (10m). A matching transformer (49:1 unun) handles the impedance transformation at the feed point.
Feed line matters too. A perfectly resonant antenna connected to poorly matched or high-loss feed line still loses power. Use the Coax Cable Loss Calculator to evaluate how much of your transmitter output actually reaches the antenna for your cable type and run length — especially important on VHF and UHF where loss increases sharply with frequency.
Safety: Before transmitting, verify that your station's RF emission levels comply with FCC Part 97.13(c)(1). The minimum safe operating distance from your antenna depends on transmitter power, antenna gain, and duty cycle — use the RF Exposure Calculator below to check compliance.
Related radio tools: Before transmitting, use the Band Plan Checker to confirm that your target frequency is within a band segment your license class permits. Calculate feed line loss for your cable type and run length with the Coax Cable Loss Calculator — the power actually delivered to your antenna may be meaningfully less than your transmitter output. Then verify your station's RF safety compliance with the RF Exposure Calculator using the effective radiated power after feed line loss.
This tool was created by Ben Crittenden, an IT professional with experience in web development, systems administration, and project management.