Free Wavelength Frequency Calculator
Convert between wavelength and frequency for any wave using the relation c = λ·f. Enter one value and the calculator solves for the other, with an editable wave speed that defaults to the speed of light.
Choose what to enter — the calculator solves the other from c = λ · f.
c = λ · f → f = c / λ and λ = c / f. Use meters for λ and hertz for f. Default c is the speed of light in a vacuum; change it for sound (≈343 m/s) or waves in a medium.
Quick answer
Wavelength and frequency are linked by the equation c = λ·f, where c is the wave's propagation speed, λ is wavelength, and f is frequency. To find frequency, divide the speed by the wavelength (f = c / λ); to find wavelength, divide the speed by the frequency (λ = c / f). For light in a vacuum, c = 299,792,458 m/s, so a 1-meter wave has a frequency of about 2.9979×10⁸ Hz.
Formula & method
c = λ · f
- c — Wave propagation speed (m/s) — 299,792,458 m/s for light in a vacuum
- λ — Wavelength (meters) — distance between successive crests
- f — Frequency (hertz) — cycles per second
The wave equation: a wave's speed equals its wavelength times its frequency. Rearrange to solve for whichever quantity is unknown.
f = c / λ and λ = c / f
Solve for frequency by dividing speed by wavelength, or for wavelength by dividing speed by frequency. Speed and wavelength must use the same length unit (meters).
Examples
- Input
- λ = 1 m, c = 299,792,458 m/s
- Result
- f ≈ 2.99792×10⁸ Hz (299,792,458 Hz)
- Why
- f = c / λ = 299,792,458 / 1 = 299,792,458 Hz, which is about 2.9979×10⁸ Hz, or roughly 300 MHz. This is the default case shown when the calculator loads.
- Input
- λ = 500 nm = 500×10⁻⁹ m = 5×10⁻⁷ m, c = 299,792,458 m/s
- Result
- f ≈ 5.99585×10¹⁴ Hz
- Why
- f = c / λ = 299,792,458 / 5×10⁻⁷ = 5.99585×10¹⁴ Hz (about 600 THz). Note that you must convert nanometers to meters first: 500 nm = 0.0000005 m.
- Input
- f = 100 MHz = 1×10⁸ Hz, c = 299,792,458 m/s
- Result
- λ ≈ 2.99792 m
- Why
- λ = c / f = 299,792,458 / 1×10⁸ = 2.99792 m. A 100 MHz FM signal has a wavelength of about 3 meters, which is why FM antennas are sized on that scale.
- Input
- f = 440 Hz (musical note A4), c = 343 m/s (speed of sound in air)
- Result
- λ ≈ 0.779545 m
- Why
- λ = c / f = 343 / 440 = 0.779545 m, about 78 cm. Here the editable speed field is set to 343 m/s — the speed of sound in 20 °C air — instead of the speed of light, because sound is a mechanical wave.
When to use this tool
- Converting the wavelength of light, radio, microwaves, or X-rays into a frequency, or vice versa, in physics and chemistry coursework.
- Sizing antennas or analyzing RF and wireless signals, where wavelength sets the physical dimensions for a given frequency band.
- Working out the wavelength of sound waves in air or another medium by setting the wave speed to that medium's value.
- Checking spectroscopy or optics problems, where photon wavelength and frequency must be interconverted before computing energy.
Common mistakes
- Mixing length units — entering wavelength in nanometers or centimeters while the speed is in meters per second. Convert wavelength to meters first (e.g. 500 nm = 5×10⁻⁷ m).
- Mixing frequency units — typing a value in MHz or GHz instead of hertz. The calculator expects plain hertz, so 100 MHz must be entered as 100000000 (1×10⁸).
- Forgetting to change the wave speed for non-light waves. The 299,792,458 m/s default is only correct for electromagnetic waves in a vacuum; use about 343 m/s for sound in air or the medium's actual speed for waves in glass, water, etc.
- Entering zero (or leaving the field blank) for wavelength or frequency — division by zero is undefined, so the calculator cannot solve for the other quantity.
Frequently asked questions
What is the formula linking wavelength and frequency?
The wave equation c = λ·f relates them, where c is the wave speed, λ is wavelength, and f is frequency. Rearranged, frequency is f = c / λ and wavelength is λ = c / f. For light in a vacuum, c is the speed of light, 299,792,458 m/s.
Are wavelength and frequency inversely proportional?
Yes. For a fixed wave speed, wavelength and frequency are inversely proportional: as one doubles, the other halves. That is a direct consequence of c = λ·f, since their product must stay equal to the constant speed c.
How do I convert nanometers or megahertz before using this tool?
Convert wavelength to meters: 1 nm = 1×10⁻⁹ m, so 500 nm = 5×10⁻⁷ m. Convert frequency to hertz: 1 MHz = 1×10⁶ Hz and 1 GHz = 1×10⁹ Hz, so 2.4 GHz = 2,400,000,000 Hz. The calculator works entirely in meters and hertz.
Why does the calculator let me edit the wave speed?
Because c = λ·f applies to any wave, not just light. Light in a vacuum travels at 299,792,458 m/s, but sound in air is about 343 m/s and light slows down in glass or water. Editing the speed lets you handle sound waves, waves in a medium, or a refractive index.
What is the frequency of visible light?
Visible light spans roughly 380 nm to 750 nm in wavelength, which corresponds to about 4.0×10¹⁴ Hz (red) up to 7.9×10¹⁴ Hz (violet). Using f = c / λ, green light near 500 nm comes out to about 6.0×10¹⁴ Hz.
Does this also give the energy of a photon?
Not directly — this tool only converts between wavelength and frequency. To get photon energy, multiply the frequency by Planck's constant (E = h·f, with h ≈ 6.626×10⁻³⁴ J·s) once you have the frequency from this calculator.
Sources & references
External references open in a new tab. We are independent and not affiliated with these organizations.
- ✓ Free to use
- ✓ No sign-up required
- ✓ Runs entirely in your browser — nothing is uploaded.
- ✓ Formula and method shown above
Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.
Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.
Related tools
- Ohm's Law CalculatorScience & Engineering
- Kinetic Energy CalculatorScience & Engineering
- Potential Energy CalculatorScience & Engineering
- Scientific CalculatorScience & Engineering
- Ideal Gas Law CalculatorScience & Engineering
Embed this tool on your site
Free to embed, no sign-up. Paste this code where you want the wavelength frequency calculator to appear: