Published on 10/13/2026
An antenna designer needs a quarter-wave monopole at 868 MHz, a stub length at 2.4 GHz and the distance between two patch elements at 5.8 GHz. The calculator is slow and the formula is simple, but the numbers come up in every RF design. This table lists the free-space wavelength and common fractions for the frequencies you use most, from 1 MHz to 40 GHz.
Short answer: wavelength in meters is 299.8 divided by frequency in MHz. At 2.4 GHz it is 12.5 cm, at 5.8 GHz 5.17 cm and at 28 GHz 10.7 mm. Inside coax, multiply by the velocity factor (0.66 for solid PE, 0.70 for PTFE).
The table also gives quarter-wave lengths in free space and in coax, since those are the numbers you cut to.
On This Page
| Frequency | Wavelength (free space) | Quarter wave (free space) | Quarter wave in PE coax (VF 0.66) | Quarter wave in PTFE coax (VF 0.70) |
|---|---|---|---|---|
| 1 MHz | 299.8 m | 74.9 m | 49.5 m | 52.5 m |
| 10 MHz | 30.0 m | 7.49 m | 4.95 m | 5.25 m |
| 30 MHz | 9.99 m | 2.50 m | 1.65 m | 1.75 m |
| 100 MHz | 3.00 m | 74.9 cm | 49.5 cm | 52.5 cm |
| 144 MHz | 2.08 m | 52.0 cm | 34.4 cm | 36.4 cm |
| 433 MHz | 69.2 cm | 17.3 cm | 11.4 cm | 12.1 cm |
| 868 MHz | 34.5 cm | 8.6 cm | 5.7 cm | 6.0 cm |
| 915 MHz | 32.8 cm | 8.2 cm | 5.4 cm | 5.7 cm |
| 1 GHz | 30.0 cm | 7.5 cm | 4.9 cm | 5.2 cm |
| 1.575 GHz (GPS L1) | 19.0 cm | 4.8 cm | 3.1 cm | 3.3 cm |
| 2.4 GHz | 12.5 cm | 3.1 cm | 2.1 cm | 2.2 cm |
| 3.5 GHz | 8.6 cm | 2.1 cm | 1.4 cm | 1.5 cm |
| 5 GHz | 6.0 cm | 1.5 cm | 9.89 mm | 1.0 cm |
| 5.8 GHz | 5.2 cm | 1.3 cm | 8.53 mm | 9.05 mm |
| 10 GHz | 3.0 cm | 7.49 mm | 4.95 mm | 5.25 mm |
| 18 GHz | 1.7 cm | 4.16 mm | 2.75 mm | 2.91 mm |
| 24 GHz | 1.2 cm | 3.12 mm | 2.06 mm | 2.19 mm |
| 28 GHz | 1.1 cm | 2.68 mm | 1.77 mm | 1.87 mm |
| 40 GHz | 7.49 mm | 1.87 mm | 1.24 mm | 1.31 mm |
Based on c = 299,792,458 m/s. Practical antenna lengths are 2 to 5 percent shorter than the free-space quarter wave because of end effects, so always tune and measure.
Key idea: Physical length in a cable is shorter than free-space length. Always use the velocity factor of the cable you use. See the velocity factor table in this series.
Phase-matched and length-critical assemblies
Tell us the frequency, length tolerance and connectors. We build and sweep each assembly on a VNA for VSWR and insertion loss before shipment.
Talk to an Engineer| Application | Length used |
|---|---|
| Monopole and whip antennas | Quarter wave |
| Dipole antennas | Half wave (two quarter-wave arms) |
| Stubs, baluns and matching | Quarter or eighth wave in cable |
| PCB trace length matching | Fraction of wavelength in the dielectric |
| Cable length and phase | Wavelengths in cable at the highest frequency |
| Spacing of array elements | About half a wavelength in free space |
A cable longer than about one tenth of a wavelength acts as a transmission line and needs proper impedance matching. At 2.4 GHz that is about 12 mm in free space and 8 mm in PTFE coax. For more on cable length in wavelengths, see the length guide on this blog.
Avoid
What is the wavelength at 2.4 GHz?
About 12.5 cm (125 mm) in free space, and about 8.7 cm in PTFE coax (VF 0.70).
What is the wavelength at 5.8 GHz?
About 5.17 cm in free space.
How do I calculate wavelength from frequency?
Divide 299.8 by the frequency in MHz to get meters.
What is a quarter wave at 433 MHz?
About 17.3 cm in free space.
What is the wavelength at 28 GHz?
About 10.7 mm in free space.
Is wavelength shorter in coax cable?
Yes. It is shorter by the velocity factor, for example 0.66 for solid PE and 0.70 for PTFE.
Divide 299.8 by the frequency in MHz, then scale by the velocity factor for cable and by the fraction you need. Verify the finished part on a VNA.
SigmaRF builds length-critical assemblies in India (Vadodara) and the USA (Cleveland area), VNA-swept before shipment, with lead times as short as 2 days.
Order a length-critical assembly
Send the frequency and tolerance.
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