100 MHz in vacuum
λ = v ÷ f
Convert 100 MHz to 100,000,000 Hz. Divide 299,792,458 m/s by that frequency to get 2.99792458 m. The default six-place display is approximately 2.997925 m. Its period is 10 ns.
Waves & oscillations
Frequency & Wavelength Calculator
Find wavelength, frequency, or wave speed from the other two quantities. See the period and equivalent SI values together.
Calculate frequency, wavelength, or wave speed
Wavelength
Enter two positive quantities, then select Calculate.
- Wavelength (SI)
- Frequency (SI)
- Wave speed (SI)
- Period (1 ÷ frequency)
- Formula
≈ marks display rounding. Period automatically uses s, ms, µs, ns, or ps for readability. Calculations run in your browser. Press Enter to calculate. Successful results appear in this tab's Recent calculations.
Three worked examples
A 0.5 m wave at 340 m/s
f = v ÷ λ
With an entered speed of 340 m/s and wavelength of 0.5 m, the frequency is 680 Hz. Here 340 m/s is a supplied example value, not an automatic estimate for air.
250 Hz with a 1.2 m wavelength
v = f × λ
Multiply 250 Hz by 1.2 m to obtain 300 m/s. The corresponding period is 4 ms. This mode solves the speed directly and does not apply the vacuum preset.
Formula, units, and calculation rules
For a periodic traveling wave, wave speed v, frequency f, and wavelength λ satisfy v = fλ. The period T is 1/f. At a fixed frequency, changing the wave speed changes the wavelength in the same proportion. This relationship uses the speed of the wave's repeating pattern (phase speed).
This tool converts inputs to hertz, meters, and meters per second before solving. It uses exact fractions for finite decimal inputs and exact unit factors, including 1 ft = 0.3048 m and 1 in = 0.0254 m. Rounding is applied only to displayed values, with halfway values rounded away from zero. Display precision is not measurement uncertainty or a significant-figure rule.
All entered quantities must be positive. Each value accepts up to 15 integer digits and 10 decimal digits, within 64 characters. The calculator does not infer refractive index, temperature, material properties, dispersion, or radio channel assignments. A mathematical result alone does not establish that a proposed wave can propagate under particular conditions.
References: OpenStax: Traveling Waves for the wave relationship and period; NIST: the meter and the fixed vacuum speed of light; NIST unit conversion factors. See our calculation policy for shared input and rounding rules.
Common questions
Is the vacuum preset suitable for sound?
No. The preset is the speed of electromagnetic waves in vacuum. For sound, enter the speed appropriate to the material and conditions you are using. This calculator does not estimate sound speed from temperature.
Can I convert a frequency to a wavelength without a speed?
A speed must be specified. The same frequency can correspond to different wavelengths in different media. Confirm the wave speed before interpreting the result.
Why do frequency and period have different units?
Frequency counts cycles per second, while period measures the time for one cycle. The period display automatically selects seconds, milliseconds, microseconds, nanoseconds, or picoseconds using the unrounded value.
Why does a small SI value show ≈ 0?
The positive value is smaller than the selected decimal precision can display. Increase the decimal places or choose a more suitable main result unit, such as nm for a short wavelength. The calculation retains the unrounded value even when its displayed SI equivalent rounds to zero.
Does the tool restrict every calculated speed to light speed?
No. It applies v = fλ to the supplied positive numbers without deciding which physical wave or material they describe. In particular, phase speed and signal speed need not be interchangeable. Check the model and measurements for your application.