Frequency Converter

Frequency Converter — Convert Hz, kHz, MHz, GHz, RPM & More

The Frequency Converter by Toolsiro converts between 9 frequency units instantly — Hertz, Kilohertz, Megahertz, Gigahertz, Terahertz, RPM, RPS, Radians per second, and CPM. It includes a quick-reference panel covering common real-world frequencies from AC power (50/60 Hz) to WiFi (2.4 and 5 GHz) to musical notes (A440).

Frequency is the number of occurrences of a repeating event per unit of time. It appears in electronics, communications, acoustics, mechanical engineering, medicine, and physics. The same physical concept — cycles per second — is measured in dramatically different units depending on the field, from the sub-hertz oscillations of ocean tides to the terahertz frequencies of visible light.

The Hertz — Cycles Per Second

The Hertz (Hz) is the SI unit of frequency, named after Heinrich Rudolf Hertz, the German physicist who first conclusively proved the existence of electromagnetic waves in 1886. One Hertz means one cycle per second — one complete oscillation, wave, rotation, or repetitive event occurring once every second.

The range of frequencies encountered in different fields spans an enormous scale. Human hearing covers approximately 20 Hz to 20,000 Hz (20 kHz). The electrical grid in most of the world oscillates at 50 Hz; in North America and some other countries, it runs at 60 Hz. AM radio broadcasts at 530 kHz to 1,700 kHz. FM radio operates at 87.5 MHz to 108 MHz. WiFi uses 2.4 GHz and 5 GHz bands. 5G mobile networks reach up to 86 GHz. The frequency of visible light spans roughly 430 THz (red) to 770 THz (violet).

The Metric Prefix Scale

Frequency units follow the standard SI metric prefix system. 1 Kilohertz (kHz) = 1,000 Hz. 1 Megahertz (MHz) = 1,000,000 Hz = 1,000 kHz. 1 Gigahertz (GHz) = 1,000,000,000 Hz = 1,000 MHz. 1 Terahertz (THz) = 10¹² Hz = 1,000 GHz. Each step represents a factor of 1,000, spanning twelve orders of magnitude from Hz to THz.

Choosing the right unit for a given frequency avoids awkward numbers. A 2.4 GHz WiFi signal is more clearly expressed as 2.4 GHz than as 2,400,000,000 Hz or 2,400,000 kHz or 2,400 MHz — though all are correct. Similarly, human hearing's upper limit of 20 kHz is cleaner than 20,000 Hz. This converter lets you see all representations simultaneously.

RPM and RPS — Rotational Frequency

Revolutions per minute (RPM) and revolutions per second (RPS) describe the rotational speed of mechanical systems. While not strictly SI units, they are universally used in engineering and everyday contexts. An automobile engine at idle typically runs at 600–900 RPM. Highway cruising might be 2,000–3,000 RPM. Red line (maximum safe RPM) for most passenger cars is 5,500–7,000 RPM. A drill might spin at 1,000–3,000 RPM for general work. A dentist's drill runs at 300,000–500,000 RPM.

Converting RPM to Hz reveals the actual frequency: 3,600 RPM ÷ 60 = 60 Hz. This is why synchronous AC motors in 60 Hz countries often run at 3,600 RPM — the motor speed is directly tied to the grid frequency. In 50 Hz countries, the equivalent speed is 3,000 RPM. This relationship between electrical frequency and mechanical rotation is fundamental to AC motor design.

Radians Per Second — Angular Frequency

Angular frequency (radians per second, rad/s) is the physicist's preferred expression of rotational frequency. While RPM counts complete revolutions, angular frequency measures the angle swept per second in radians. Since one complete revolution equals 2π radians, converting between Hz and rad/s requires multiplying or dividing by 2π (approximately 6.2832).

Angular frequency appears in differential equations of oscillation, AC circuit analysis (impedance calculations), control systems, signal processing, and quantum mechanics. When an engineer writes ω = 2πf, ω (omega) is the angular frequency in rad/s and f is the frequency in Hz. For a 60 Hz power system, ω = 2π × 60 ≈ 377 rad/s.

Frequency in Electronics and Communications

Electronic circuits, radio communications, and digital systems are defined by their operating frequencies. A processor's clock speed — 3.5 GHz in a modern computer — represents 3.5 billion clock cycles per second, each cycle capable of executing part of an instruction. Higher clock speeds generally mean faster processing, though the relationship is complex.

Radio frequencies are divided into bands allocated for different uses. AM radio operates in the Medium Frequency (MF) band at 300 kHz–3 MHz. FM radio, TV broadcasting, and aviation communications use the VHF band (30–300 MHz). Cellular networks, WiFi, Bluetooth, and GPS operate in the UHF band (300 MHz–3 GHz) and SHF band (3–30 GHz). Radar systems span VHF to EHF. Understanding frequency bands requires converting between Hz, kHz, MHz, and GHz constantly.

Frequency in Medicine and Biology

Biological and medical systems operate across a wide frequency range. The human heart beats at 60–100 times per minute in a resting healthy adult — 1 to 1.67 Hz. Brainwaves (EEG signals) range from 0.5 Hz (delta waves in deep sleep) to over 100 Hz (gamma waves during intense cognitive activity). Ultrasound imaging uses frequencies of 2–18 MHz. MRI machines use radiofrequency pulses in the MHz range (for most clinical systems, 63.9 MHz for 1.5 Tesla or 127.7 MHz for 3 Tesla systems).

Frequency in Music and Acoustics

Musical notes are defined by their frequencies. The standard tuning pitch A4 (the A above middle C) is 440 Hz — this is why the quick preset is labeled "A440." Each musical octave doubles the frequency: A3 is 220 Hz, A4 is 440 Hz, A5 is 880 Hz. The piano's lowest note (A0) is 27.5 Hz; the highest (C8) is 4,186 Hz.

Acoustic frequency and perceived pitch are directly related, but the relationship is logarithmic in human perception. The difference between 100 Hz and 200 Hz sounds the same as the difference between 1,000 Hz and 2,000 Hz — both are one octave. This logarithmic perception is why musical scales and audio engineering work in octaves and decibels rather than linear frequency increments.

Frequently Asked Questions

What is the difference between Hz and RPM? Hz (Hertz) measures complete cycles per second. RPM measures complete revolutions per minute. To convert RPM to Hz, divide by 60. To convert Hz to RPM, multiply by 60. 3,000 RPM = 50 Hz; 3,600 RPM = 60 Hz.

What frequency does WiFi use? Standard WiFi operates in the 2.4 GHz band (2,400–2,484 MHz) and the 5 GHz band (5,180–5,850 MHz). WiFi 6E also uses the 6 GHz band. The 2.4 GHz band has better range; the 5 GHz band has higher speeds but shorter range.

What is the frequency of visible light? Visible light spans approximately 430 THz (red, ~700 nm wavelength) to 770 THz (violet, ~390 nm wavelength). Infrared is below 430 THz; ultraviolet is above 770 THz. Frequency and wavelength are related by the speed of light: f = c/λ.

What does angular frequency (rad/s) mean and how is it related to Hz? Angular frequency (ω) measures rotation in radians per second. One full cycle = 2π radians, so ω = 2πf. For 50 Hz: ω = 2π × 50 ≈ 314 rad/s. For 60 Hz: ω ≈ 377 rad/s.

Frequency and Wavelength

For electromagnetic waves (radio, light, X-rays) and sound waves, frequency and wavelength are inversely related through wave speed. For electromagnetic waves in vacuum: wavelength (λ) = speed of light (c) / frequency (f) = 299,792,458 m/s ÷ f. A 2.4 GHz WiFi signal has a wavelength of about 12.5 cm, which explains why small antennas work at these frequencies. A 100 MHz FM radio signal has a wavelength of about 3 meters. Visible light at 500 THz has a wavelength of 600 nm (nanometers).

For sound in air at 20°C: wavelength = 343 m/s ÷ frequency. A 440 Hz tone (musical A) has a wavelength of about 0.78 meters. A 20 Hz bass note has a wavelength of about 17 meters — longer than a typical room, which is why bass is difficult to control acoustically. A 20 kHz ultrasonic note has a wavelength of about 1.7 cm, about the width of a finger.