Wavelength ↔ Frequency Calculator - EM & Sound Waves

How to use this tool

Select Light / EM, Sound, or Custom speed. Custom mode needs a positive speed; approximate air, water, steel, and soft-tissue presets are available.
Enter a wavelength or frequency and choose its unit.
The other value, period, and applicable photon or spectrum results update instantly.

Wave equation

v = λ × f - wave speed equals wavelength times frequency. For EM waves in a vacuum, v = c = 299,792,458 m/s. For sound in air at 20°C, v ≈ 343 m/s.

This relationship describes both electromagnetic and mechanical waves, but the speed depends on the wave and its medium. Select Light / EM, Sound, or enter a positive Custom speed. The optional air, water, steel, and soft-tissue presets are approximate examples; real values vary with temperature and material. The calculator uses the selected speed in the equation and does not treat sound or a custom-speed wave as light.

EM spectrum regions

Gamma ray: <0.01 nm
X-ray: 0.01–10 nm
Ultraviolet: 10–400 nm
Visible light: 400–700 nm
Infrared: 700 nm–1 mm
Microwave: 1 mm–10 cm
Radio wave: >10 cm

Sound wave context

Unlike electromagnetic waves, sound waves are longitudinal mechanical waves that require a medium. In air at 20°C, sound travels at approximately 343 m/s. Using the wave equation:

Concert A pitch (440 Hz): λ = 343 / 440 ≈ 0.78 m
Bass guitar low E (41 Hz): λ ≈ 8.4 m
Ultrasound imaging (2 MHz): λ = 1,540 / 2,000,000 ≈ 0.00077 m, or 0.77 mm, in soft tissue

Sound travels faster in denser media: ~1,480 m/s in water and ~5,120 m/s in steel.

Visible light and colour

Human vision can respond to roughly 380–750 nm, depending on the observer and conditions. For consistency with this calculator's EM-region label, the colour guide below uses its simpler 400–700 nm visible band. The swatch is an approximate teaching aid, not a precise colourimeter:

Colour	Wavelength range
Violet	400–450 nm
Blue	450–495 nm
Green	495–570 nm
Yellow	570–590 nm
Orange	590–620 nm
Red	620–700 nm

Sunsets appear red/orange because shorter wavelengths (violet, blue) scatter more strongly in the atmosphere (Rayleigh scattering), leaving longer wavelengths to dominate at low solar angles.

Photon energy connection

For electromagnetic radiation only, photon energy connects the wave and quantum descriptions. The result panel shows this value in Light / EM mode and intentionally omits it for sound and custom waves: mechanical waves are not photons, even though they also have a wavelength and frequency.

E = h×f = h×c / λ

Where h = 6.626 × 10⁻³⁴ J·s (Planck’s constant). A 500 nm (green) photon carries approximately 2.5 eV of energy. This formula bridges classical wave physics and quantum mechanics, explaining why UV light causes sunburn (high energy) while radio waves do not.

Frequently asked questions

What is the relationship between wavelength and frequency?

Wave speed equals wavelength times frequency: v = λ × f. For electromagnetic waves in a vacuum, v = c = 299,792,458 m/s. For sound in air at 20°C, v is about 343 m/s. You can also enter a positive custom speed or use an approximate medium preset.

Why is photon energy shown only for light / EM waves?

E = h × f describes the energy of an electromagnetic photon. Sound and other mechanical waves can have frequency and wavelength, but they are not photons, so this calculator intentionally omits a photon-energy value in those modes.