Wavelength Calculator
Wavelength, quarter wave, and period from any frequency.
What it does
Wavelength divides light speed by frequency: higher frequencies pack shorter waves. Radio engineers read meters for antennas while the period in nanoseconds times the same math for timing.
The tool above takes the frequency from hertz to gigahertz. It returns meters with the quarter wave antenna length and the period beside them.
The default 100 MHz spans 2.9979 m (quarter 0.7495 m) with a 10 ns period. Wifi at 2.4 GHz shrinks to 0.1249 m with 0.42 ns per cycle by the same division.
Light speed is exact at 299,792,458 m/s per NIST references with FCC frequency bands measured the same way. Sound waves need 343 m/s instead and sit outside this page.
How to use
- Enter the frequency number.
- Pick Hz, kHz, MHz, or GHz to match it.
- Read meters first for the wave length.
- Use quarter wave for whip antenna cuts.
- Use period for timing and scope math.
Formula
- c
- 299,792,458 m/s exact vacuum light speed.
- /4
- Resonant whip fraction for antennas.
- 1/f
- Seconds per single cycle.
Vacuum electromagnetic waves assumed throughout. Cables slow waves by their velocity factor, so cut coax longer than free space math.
Worked example
Example: 100 MHz
Frequency 100 MHz.
- Hertz: 100 x 1,000,000 = 100,000,000 Hz.
- Wavelength: 299,792,458 / 100,000,000 = 2.9979 m.
- Quarter: 2.9979 / 4 = 0.7495 m.
- Period: 1 / 100,000,000 = 10 ns.
- Tool shows 2.9979 m, 0.7495 m, 10 ns.
Reference table
| Service | Frequency | Wavelength |
|---|---|---|
| FM radio | 100 MHz | 3 m |
| Wifi 2.4G | 2.4 GHz | 12.5 cm |
| Wifi 5G | 5 GHz | 6 cm |
| GPS L1 | 1575 MHz | 19 cm |
Limits
- Vacuum EM only; sound and cable speeds differ.
- Antenna math idealizes ground and surroundings.
- Period auto scales units for readability.
- Dispersive media shift real wavelengths.
Common mistakes
- Entering MHz as Hz (millionfold error).
- Using 343 m/s sound speed for radio.
- Cutting whips to full wave instead of quarter.
- Forgetting velocity factor in coax.
- Reading period in wrong auto units.
Try it yourself
Quick checks. Answers sit tucked under each question.
2.4 GHz wavelength?
299792458 / 2.4e9 = 0.1249 m.
Quarter of 0.1249 m?
0.0312 m, about 3 cm.
Period of 100 MHz?
1 / 1e8 = 10 ns.
Questions
How do you find wavelength?
Divide light speed by hertz: 100 MHz gives 2.9979 m.
What is quarter wave?
Wavelength over four: the classic whip length, 0.7495 m here.
Why nanoseconds?
Radio periods run billionths of seconds; auto units keep them readable.
Sound too?
No. Sound needs 343 m/s, a different page entirely.
Does cable change it?
Yes by velocity factor near 0.66 to 0.85; cut longer.
Exact light speed?
299,792,458 m/s, exact by SI definition.