How it works
Wavelength is the physical distance between wave crests: wave speed divided by frequency. For light and radio, speed is the speed of light (299,792,458 m/s); for sound in air it's about 343 m/s.
The default values show WiFi: at 2.4 GHz the wavelength is 12.5 cm. That size determines everything about the signal's behaviour — how it bends around furniture, passes through walls, and why router antennas are a few centimetres long (antennas work best at simple fractions of the wavelength).
Wavelength explains daily mysteries: why 5 GHz WiFi is faster but weaker through walls (shorter waves penetrate less), why submarines need kilometre-long radio waves, and why a microwave oven's 12.2 cm waves excite water molecules so well.
Use it in real life
Home WiFi: 2.4 GHz (12.5 cm) travels through walls better; 5 GHz (6 cm) carries more data but fades faster. Physics — not marketing — decides which band to pick per room.
Music and rooms: a 50 Hz bass note in air is 6.9 m long — comparable to your living room, which is why bass 'booms' in some spots and vanishes in others (standing waves).
Microwave ovens operate at 2.45 GHz; the hot/cold spots in un-rotated food sit half a wavelength (~6 cm) apart. The turntable exists because of this equation.
Frequently asked questions
What's the wavelength of visible light?
About 380–750 nanometres — violet is short, red is long. That's roughly one hundredth the width of a human hair, which is why light seems to travel in perfect straight lines at human scale.
How long are sound wavelengths?
In air (343 m/s): a 20 Hz deep bass wave is 17 m long; a 20 kHz treble wave just 1.7 cm. This ratio is why bass fills a room while treble is directional.
Why do antennas relate to wavelength?
Antennas resonate — they transmit and receive best when their length is a simple fraction (commonly ¼ or ½) of the wavelength. FM radio (~3 m waves) wants ~75 cm antennas; WiFi (~12.5 cm) needs only ~3 cm.