Wavelength Calculator

Quick Answer

Last updated: 3 November 2026 ·How we calculate this: v = f × λ

How This Wavelength Calculator Works

Choose whether you want the wavelength or the frequency, then pick the kind of wave. Light, radio waves, microwaves and X-rays all travel at the speed of light in a vacuum. Sound in air at room temperature travels at about 343 m/s. For any other wave, such as sound in water or a wave on a string, choose another speed and type it in.

Enter the frequency or the wavelength in the unit you have. The calculator converts it to hertz or meters, uses the wave equation, and shows the answer in several units with the period of one cycle. For light and other electromagnetic waves, it also gives the energy of one photon.

How to Use the Wavelength Calculator

1. Choose whether to solve for wavelength or frequency.
2. Pick light or radio, sound in air, or another wave speed.
3. Enter the frequency or wavelength and choose its unit.
4. Press Calculate.
5. Read the wavelength, frequency, period and, for light, photon energy.

Core Formulas

• Wave speed: v = f × λ
• Wavelength: λ = v ÷ f
• Frequency: f = v ÷ λ
• Period: T = 1 ÷ f
• Photon energy: E = h × f = h × c ÷ λ

c = 299,792,458 m/s and h = 6.62607015 × 10⁻³⁴ J·s are exact values in the SI. One electronvolt is 1.602176634 × 10⁻¹⁹ J.

Key Terms

• Wavelength (λ): the length of one full wave cycle.
• Frequency (f): the number of cycles per second, in hertz.
• Period (T): the time for one cycle, equal to 1 ÷ f.
• Photon: a single packet of light energy.
• Electronvolt (eV): a small unit of energy, 1.602176634 × 10⁻¹⁹ J.

Worked Example

Green light has a wavelength of about 500 nm. What are its frequency and photon energy?

• λ = 500 nm = 5 × 10⁻⁷ m
• f = 299,792,458 ÷ (5 × 10⁻⁷) = 5.99585 × 10^14 Hz
• E = h × f = 3.97289 × 10^-19 J, which is about 2.4797 eV

Real-Life Examples

• FM radio: a 100 MHz station has a wavelength of about 3 m.
• Wi-Fi: 2.4 GHz waves are about 12.49 cm long.
• Music: the note A at 440 Hz has a wavelength of 0.7795 m in air at 20 °C.
• Lasers: a 650 nm red laser has a frequency of 4.61219 × 10^14 Hz.

Wavelength vs Frequency

• Wavelength: the distance between two matching points on a wave, in meters.
• Frequency: how many waves pass each second, in hertz.
• Inverse link: at a fixed speed, one goes up as the other goes down.

Common Waves

What Changes a Wave’s Speed

• The medium: light slows down in glass and water. Sound is faster in water and solids than in air.
• Temperature: sound in air speeds up as the air gets warmer, from about 331 m/s at 0 °C to 343 m/s at 20 °C.
• Frequency stays the same: when a wave enters a new medium, its frequency does not change, so its wavelength changes instead.
• Tension and mass: on a guitar string, a tighter or lighter string carries waves faster.

Wavelength Across the Spectrum

Electromagnetic waves cover a huge range. Radio waves can be many meters or even kilometers long, microwaves are centimeters to millimeters, visible light is a few hundred nanometers, and X-rays are far smaller than an atom is wide. All of them travel at the same speed in a vacuum, so the only thing that tells them apart is frequency, or wavelength.

Sound waves are mechanical. They need air, water or a solid to travel through, and they are far slower. Human hearing covers roughly 20 Hz to 20 kHz, which in air is wavelengths from about 17 m down to about 1.7 cm.

Common Mistakes to Avoid

• Mixing units. MHz is a million hertz, and nm is a billionth of a meter. Choose the units here instead of converting by hand.
• Using the speed of light for sound. Sound is almost a million times slower.
• Thinking frequency changes in a new medium. It is the speed and wavelength that change.
• Forgetting temperature for sound. 343 m/s is for 20 °C air only.
• Mixing up period and frequency. Period is seconds per cycle; frequency is cycles per second.

Frequently Asked Questions

References & Sources