Frequency is the number of cycles per second, in hertz. Middle A on a piano is 440 Hz, Wi-Fi uses 2.4 and 5 GHz, and green light oscillates at about 560 THz. The wave speed and wavelength together fix the frequency.
How to use the Frequency Calculator
- Wave velocity of
- Wave velocity v
- Wavelength λ
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Pick the medium to fill in the wave speed (or choose a custom speed), then enter the wavelength.
Inputs explained
| Field | What to enter |
|---|---|
| Wave velocity of | Choose one: Light in vacuum, Light in air, Light in water, Light in glass … |
| Wave velocity v | Units: m/s, km/h, mph, ft/s, knots, km/s |
| Wavelength λ | Units: m, cm, mm, µm, nm, km … |
What each result means
- Frequency f = [v]÷[Wavelength λ]
- Period T = [Wavelength λ]÷[v]
- Angular frequency = 2×pi×[v]÷[Wavelength λ]
Example values
How the main result changes when Wave velocity v changes and everything else stays at the example values above:
| Wave velocity v (m/s) | Frequency f (Hz) |
|---|---|
| 170 | 439.7436 |
| 255 | 439.7436 |
| 340 | 439.7436 |
| 425 | 439.7436 |
| 510 | 439.7436 |
| 680 | 439.7436 |
Formula
f = v/λ, T = 1/f
Worked example
Inputs — Wave velocity of: Sound in air at 20 °C; Wavelength λ: 0.78 m.
Results — Frequency f = 439.74359 Hz; Period T = 0.002274 s; Angular frequency = 2,762.990462 rad/s.
Key terms
- Frequency
- Cycles per unit time.
Frequently asked questions
What is a hertz?
One cycle per second.
How are frequency and period related?
T = 1/f.
Does frequency change when a wave enters a new medium?
No – the speed and wavelength change, the frequency stays the same.
What is the audible frequency range?
About 20 Hz to 20 kHz for young humans.