Wavelength and Frequency Calculator

Every wave, from radio and light to sound and ocean swells, links its speed, frequency and wavelength the same way. Enter two and this calculator finds the third, in units that fit (nanometers and terahertz for light, meters and hertz for sound), along with the period and, for light, the energy of a single photon.

How to Use It

1. Choose what to Find: Wave Speed, Frequency or Wavelength.
2. Enter the other two values with their units. For light, keep the wave speed at 299,792,458 m/s; for sound in air, use about 343 m/s.
3. Choose the unit for the answer in Answer In.
4. Press Calculate to see the answer, the period and, for light, the photon energy.

How It Works

The speed of a wave is its frequency times its wavelength:

For light, the speed is $c = 299{,}792{,}458 \text{ m/s}$, so $c = f\lambda$. The period is the time for one wave, $T = \frac{1}{f}$. A photon of light carries energy $E = hf$, where Planck’s constant $h = 6.626 \times 10^{-34}$ J·s.

Worked Example

Green light with a wavelength of 500 nm:

Each photon carries $E = hf \approx 3.97 \times 10^{-19}$ J, about 2.48 eV.

Tips and Common Mistakes

• Convert nanometers to meters when working by hand: 500 nm = 500 × 10⁻⁹ m.
• Use the right wave speed. Light and sound travel at very different speeds; sound is about 343 m/s in air at 20 °C.
• Frequency doesn’t change when a wave enters a new material; its speed and wavelength do.
• Higher frequency, shorter wavelength, at the same speed.
• Photon energy grows with frequency, which is why ultraviolet light carries more energy per photon than red light.