Wavelength Calculator
This wavelength calculator finds the wavelength from a frequency, or the frequency from a wavelength. A 2.4 GHz Wi-Fi signal has a wavelength of 12.49 cm in vacuum, green light of 550 nm has a frequency of 545 THz, and concert A at 440 Hz is about 78 cm in air.
Example: Value 2.4 · Unit: GHz (frequency) · Medium: Vacuum (light, radio) → Result: Wavelength: 12.491 cm (frequency 2.4 GHz). Source: NIST – CODATA: speed of light c = 299 792 458 m/s, Planck constant h (exact SI values). Updated: .
How it is calculated
How to calculate wavelength – the formula
Wavelength and frequency are linked by the propagation speed: λ = v ÷ f and f = v ÷ λ. For light and radio waves in vacuum, v = c = 299,792,458 m/s. At 2.4 GHz that gives λ = 299,792,458 ÷ 2.4 × 10⁹ = 0.1249 m.
In air, water and glass
In matter light travels slower: v = c ÷ n with the refractive index n. The frequency stays the same and the wavelength shrinks by the factor n. Green light of 550 nm in vacuum is about 413 nm in water (n = 1.333). For sound in air at 20 °C the calculator uses 343 m/s.
Photon energy and colour
- Photon energy: E = h × f, in electronvolts roughly 1239.84 ÷ λ (in nm). 550 nm corresponds to 2.25 eV.
- Visible light: roughly 380 to 750 nm, from violet to red.
- Spectral ranges: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays; the limits are common approximations.
Limits
The refractive indices apply to visible light and change with wavelength and temperature; glass differs by type. For radio in cables or circuit boards the velocity factor of the material matters, which is not included here. Colour limits are approximations because colour perception is gradual.
Frequently asked questions
How do you calculate wavelength?
With λ = v ÷ f, propagation speed divided by frequency. For radio and light in vacuum, v is the speed of light, 299,792,458 m/s.
How do you calculate frequency from wavelength?
With f = v ÷ λ. Green light of 550 nm has f = 299,792,458 ÷ 550 × 10⁻⁹ = 545 THz in vacuum.
What is the wavelength at 2.4 GHz?
12.49 cm in vacuum. In air it is about 0.03% shorter because of the refractive index.
How do you calculate the wavelength of sound?
Speed of sound divided by frequency. In air at 20 °C it is 343 m/s, so at 440 Hz about 0.78 m.
What wavelength does visible light have?
Roughly 380 to 750 nanometres, from violet at the short end to red at the long end.
Sources and legal basis
- NIST – CODATA: speed of light c = 299 792 458 m/s, Planck constant h (exact SI values)
- Wikipedia – Electromagnetic spectrum: bands and visible-light wavelengths
- Wikipedia – Refractive index: refractive index of air, water and glass
- Wikipedia – Speed of sound: 343 m/s in air at 20 °C
As of: · Editorial policy
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