Frequency ↔ Wavelength Calculator
Convert between radio frequency and free-space wavelength, and calculate antenna dimensions for any RF signal.
Frequency input
Wavelength input
Enter a wavelength to compute the corresponding frequency. Both inputs stay in sync — editing either one updates the other.
Frequency
Free-space wavelength (λ)
Antenna dimensions (free space)
Common telecom frequencies
| Band | Frequency | λ | λ/4 |
|---|---|---|---|
| AM broadcast | 1 MHz | 300 m | 75 m |
| FM broadcast | 100 MHz | 3 m | 75 cm |
| GSM 900 | 900 MHz | 33.3 cm | 8.3 cm |
| LTE Band 3 | 1800 MHz | 16.7 cm | 4.2 cm |
| LTE Band 1 | 2100 MHz | 14.3 cm | 3.6 cm |
| LTE Band 7 | 2600 MHz | 11.5 cm | 2.9 cm |
| 5G Sub-6 | 3500 MHz | 8.6 cm | 2.1 cm |
| 5G mmWave | 28 GHz | 10.7 mm | 2.7 mm |
| 5G mmWave | 39 GHz | 7.7 mm | 1.9 mm |
| Wi-Fi 2.4 GHz | 2400 MHz | 12.5 cm | 3.1 cm |
| Wi-Fi 5 GHz | 5800 MHz | 5.2 cm | 1.3 cm |
Formulas
λ (m) = c / f where c = 299,792,458 m/s
f (Hz) = c / λ
Half-wave dipole = λ / 2
Quarter-wave whip = λ / 4
5/8-wave = 5λ / 8
Effective (coax) = λ × velocity_factor
Velocity Factor Reference
The velocity factor (VF) is the ratio at which an electromagnetic signal propagates through a medium relative to free space. It is always less than or equal to 1.00. When designing coax stubs, delay lines, or PCB trace antennas, multiply the free-space wavelength by the VF to get the correct physical cut length. See the frequency-to-band lookup to identify which cellular band your frequency falls in, or the link budget calculator for end-to-end path loss analysis.
| Medium | Velocity Factor |
|---|---|
| Free space (vacuum/air) | 1.00 |
| Open wire line | 0.97 |
| LMR-400 coax | 0.85 |
| RG-8 coax | 0.77 |
| RG-58 coax | 0.66 |
| FR4 PCB trace | ~0.50 |
Frequently Asked Questions
How do you convert frequency to wavelength?▾
The relationship is λ = c/f, where c is the speed of light (299,792,458 m/s), f is the frequency in Hz, and λ is the wavelength in metres. For example, a 1800 MHz LTE signal has λ = 299,792,458 / 1,800,000,000 = 0.1666 m = 16.66 cm. For antennas inside cables or on PCBs, multiply by the velocity factor (typically 0.66 for RG-58 coax) to get the effective electrical wavelength.
What is a half-wave dipole antenna length?▾
A half-wave dipole is the most fundamental antenna element, resonating when its total length equals one half of the signal wavelength (λ/2). At 900 MHz (GSM), λ/2 ≈ 16.6 cm. At 1800 MHz (LTE Band 3), λ/2 ≈ 8.3 cm. In practice, the antenna is cut slightly shorter (by a factor of ~0.95) to account for end effects and the finite wire diameter, which raises the resonant frequency slightly.
Why are 5G mmWave antennas so small?▾
At 28 GHz, the wavelength is only 10.7 mm, making λ/2 ≈ 5.4 mm. This extreme miniaturisation allows dozens or hundreds of antenna elements to fit in a compact array — enabling the massive MIMO and beamforming techniques that give 5G mmWave its multi-Gbps throughput. The trade-off is increased free-space path loss and reduced diffraction around obstacles.
What is velocity factor and why does it matter?▾
Velocity factor (VF) is the ratio of signal propagation speed inside a medium to the speed of light in vacuum. In RG-58 coaxial cable, VF ≈ 0.66 — the signal travels at 66% of c. A λ/4 stub cut for free space would be too long; it must be shortened by the VF to resonate correctly. VF is essential for designing coax stubs, delay lines, and PCB trace antennas.