Frequency Converter

Free Online Frequency Converter — Hz, kHz, MHz, GHz, RPM, and Radians per Second

Frequency is the measure of how often a repeating event occurs per unit of time, and it appears in a remarkable diversity of technical and scientific contexts — from the imperceptibly slow oscillations of geological phenomena to the terahertz vibrations of molecular bonds. Each of these domains has its own preferred unit: audio engineers work in hertz and kilohertz, RF engineers in megahertz and gigahertz, mechanical engineers in RPM (revolutions per minute), control engineers in radians per second, and power engineers in Hz. Our free online frequency converter handles all of these unit families in one place, making cross-domain frequency calculations fast and error-free.

Hertz — The Universal SI Unit of Frequency

The hertz (Hz) is the SI unit of frequency, defined as one cycle per second (1 Hz = 1 s⁻¹). It was named in honor of Heinrich Rudolf Hertz, the German physicist who first conclusively demonstrated the existence of electromagnetic waves in 1888. The hertz is the starting point for the full SI frequency scale: millihertz (mHz) for very slow periodic phenomena, kilohertz (kHz = 1,000 Hz), megahertz (MHz = 1,000,000 Hz), gigahertz (GHz = 10⁹ Hz), and terahertz (THz = 10¹² Hz) for increasingly high-frequency phenomena.

Hertz as a unit appears across an enormous range of physical phenomena. The human heart beats at approximately 1 Hz at rest. AC electrical power in North America oscillates at 60 Hz (50 Hz in most of the world). Audible sound spans from 20 Hz to 20 kHz. AM radio broadcasts at 530-1700 kHz. FM radio at 87.5-108 MHz. Wi-Fi at 2.4 GHz and 5 GHz. Mobile 5G at up to several tens of GHz. Infrared light at roughly 300 GHz to 430 THz. Visible light at 430-770 THz. X-rays at 30 petahertz and above. The hertz scale encompasses the entire electromagnetic spectrum and extends equally to acoustic, mechanical, and electrical oscillations.

RPM to Hz Conversion — Connecting Rotational and Oscillatory Frequency

Revolutions per minute (RPM) is the rotational frequency unit used universally in mechanical engineering, automotive engineering, and any context involving rotating machinery. Converting RPM to Hz (or hertz to RPM) is one of the most practically important frequency conversions in engineering, arising constantly in motor selection, vibration analysis, and power transmission design.

The conversion is mathematically simple: divide RPM by 60 to get hertz (revolutions per second). A motor spinning at 3,000 RPM rotates at 50 revolutions per second — exactly 50 Hz. This is not a coincidence: synchronous electric motors running on 50 Hz power typically rotate at 3,000 RPM (for a 2-pole motor) or 1,500 RPM (4-pole), 1,000 RPM (6-pole), and so on in integer divisions based on the formula RPM = (120 × frequency) / number of poles. In 60 Hz countries, the equivalent synchronous speeds are 3,600 RPM, 1,800 RPM, 1,200 RPM, and 900 RPM.

Vibration analysis is another major application of RPM-to-Hz conversion. When a rotating machine develops a bearing defect, gear wear, or imbalance, the resulting vibration occurs at frequencies related to the rotation speed. Vibration analysis software works in hertz, while machine operators describe speeds in RPM. Converting the rotation speed to Hz and its harmonics allows analysts to identify which component is generating a specific vibration frequency signature, guiding targeted maintenance decisions.

Radians per Second — Angular Frequency in Mathematics and Engineering

Angular frequency, expressed in radians per second (rad/s), is the frequency representation used in mathematics, physics, and electrical engineering for sinusoidal analysis. Angular frequency ω relates to ordinary frequency f in hertz by the equation ω = 2πf. The factor of 2π accounts for the fact that one complete cycle corresponds to 2π radians of phase angle in the sinusoidal representation of the signal.

In electrical circuit analysis, angular frequency appears naturally in impedance formulas for capacitors and inductors. Capacitive reactance is X_C = 1/(ωC) and inductive reactance is X_L = ωL, where C and L are the capacitance and inductance values. Using angular frequency rather than ordinary frequency eliminates the 2π factor from these equations, making the algebra cleaner. Transfer functions in control engineering, Fourier transforms in signal processing, and damped oscillator solutions in physics all use angular frequency as the natural variable.

Converting between rad/s and Hz is therefore a frequent requirement for engineers moving between theoretical calculations (naturally expressed in rad/s) and measurement contexts (naturally expressed in Hz). Our converter makes this transition immediate. A system resonance calculated at ω = 1,000 rad/s corresponds to f = 1,000 / (2π) ≈ 159.15 Hz — a frequency that can be verified with standard test equipment calibrated in hertz.

Radio Frequency Bands — MHz and GHz in Wireless Communication

The megahertz and gigahertz scales are the native frequency territory of wireless communication technology. Understanding which frequency bands are used for which applications, and converting between them and related wavelength measurements, is fundamental knowledge for RF engineers, telecommunications professionals, and anyone developing or deploying wireless systems.

AM broadcast radio occupies 530-1700 kHz (0.53-1.70 MHz). FM radio uses 87.5-108 MHz. VHF television channels occupy 54-216 MHz. Cellular LTE networks operate across multiple bands from roughly 700 MHz to 2.6 GHz. Wi-Fi operates in the 2.4 GHz band (2400-2484 MHz) and the 5 GHz band (5150-5850 MHz), with newer Wi-Fi 6E adding 6 GHz band support. Bluetooth uses 2.4-2.485 GHz. GPS signals are transmitted at 1.176 GHz and 1.575 GHz. Microwave ovens use 2.45 GHz — the same band as Wi-Fi, which is why proximity to a microwave oven can interfere with 2.4 GHz Wi-Fi connections.

Audio Frequency — Hertz and Kilohertz in Sound Engineering

The audible frequency range spans from approximately 20 Hz to 20 kHz (20,000 Hz), though individual hearing varies significantly with age, health, and genetics. Within this range, different frequency regions have distinct perceptual and acoustic characteristics that audio engineers, acousticians, and musicians work with daily.

The sub-bass region (20-60 Hz) contains the lowest audible frequencies — the deep rumble of bass instruments, the resonant thump of kick drums, and the foundation of movie theater sound effects. The bass region (60-250 Hz) provides the warmth and body of music. The midrange (250 Hz to 4 kHz) is where most of the fundamental frequencies of speech and common instruments lie, and where the human auditory system is most sensitive. The presence range (4-8 kHz) adds definition and attack to sounds. The air region (8-20 kHz) provides the sparkle and spaciousness that distinguishes high-quality audio reproduction from bandwidth-limited phone calls.

Frequency conversion between Hz and kHz is routine in audio production work. An equalizer's frequency bands might be labeled in Hz at low frequencies (60 Hz, 120 Hz, 250 Hz) and kHz at high frequencies (1 kHz, 4 kHz, 10 kHz, 20 kHz). Crossover frequencies in speaker system design are specified in Hz or kHz depending on where in the spectrum they fall. Sample rate specifications (44,100 Hz or 44.1 kHz, for example) describe how many audio samples per second a digital audio system captures or plays back.