Understanding Frequency Units and Conversions
Frequency measures how often a periodic event occurs per unit of time. It's measured in hertz (Hz)—cycles per second—in the SI system. Understanding frequency conversions is essential for electronics, radio communications, computing, and physics.
Quick conversions (high intent)
- 1 kHz = 1,000 Hz
- 1 MHz = 1,000,000 Hz
- 1 GHz = 1,000,000,000 Hz
- Hz = RPM / 60, RPM = Hz × 60
Common Frequency Units
- Hertz (Hz): The SI base unit for frequency. One hertz = one cycle per second. Named after Heinrich Hertz. Used for low frequencies (sound, AC power, mechanical vibrations).
- Kilohertz (kHz): Equal to 1,000 hertz. Used for radio frequencies (AM radio: 535-1,705 kHz), audio frequencies, and some electronic signals.
- Megahertz (MHz): Equal to 1,000,000 hertz or 1,000 kHz. Used for FM radio (88-108 MHz), television, and early computer processors.
- Gigahertz (GHz): Equal to 1,000,000,000 hertz or 1,000 MHz. Used for modern computer processors (2-5 GHz), Wi-Fi (2.4 GHz, 5 GHz), and cellular networks.
- RPM (Revolutions per Minute): Measures rotational frequency. One RPM = 1/60 Hz = 0.01667 Hz. Used for engines, hard drives, fans, and rotating machinery.
Conversion Reference Table
| Unit | Hertz Equivalent | Common Usage |
|---|---|---|
| 1 Hertz | 1 Hz | SI base unit, low frequencies |
| 1 Kilohertz | 1,000 Hz | AM radio, audio |
| 1 Megahertz | 1,000,000 Hz | FM radio, TV, early CPUs |
| 1 Gigahertz | 1,000,000,000 Hz | Modern CPUs, Wi-Fi, cellular |
| 1 RPM | 0.01667 Hz | Rotational speed |
Frequency Ranges by Application
Audio Frequencies
Human hearing range: 20 Hz to 20,000 Hz (20 kHz). Bass frequencies: 20-250 Hz, Midrange: 250-4,000 Hz, Treble: 4,000-20,000 Hz. Audio CDs sample at 44.1 kHz. High-quality audio uses 48 kHz or 96 kHz sampling rates.
Radio Frequencies
AM radio: 535-1,705 kHz (medium wave). FM radio: 88-108 MHz. Television: VHF 54-216 MHz, UHF 470-890 MHz. Wi-Fi: 2.4 GHz and 5 GHz bands. Cellular: 700 MHz - 3.5 GHz (varies by generation: 4G, 5G).
Computer Processors
CPU clock speeds are measured in gigahertz (GHz). Modern processors: 2-5 GHz. A 3.5 GHz processor executes 3.5 billion cycles per second. Higher frequency generally means faster processing, but efficiency and architecture also matter. Overclocking can push CPUs to 5+ GHz.
Electrical Power
AC power frequency: 60 Hz in North America, 50 Hz in Europe and most of the world. This is why some devices (like clocks) don't work correctly when moved between regions. The frequency determines how fast AC current alternates direction.
Frequency and Wavelength Relationship
Frequency and wavelength are inversely related through the speed of light: c = f × λ, where c = speed of light (299,792,458 m/s), f = frequency (Hz), λ = wavelength (m).
Examples:
- 100 MHz radio: wavelength = 3 m
- 2.4 GHz Wi-Fi: wavelength = 12.5 cm
- 5 GHz Wi-Fi: wavelength = 6 cm
- Visible light (600 THz): wavelength = 500 nm
Formula: Wavelength (m) = 299,792,458 / Frequency (Hz). Higher frequency = shorter wavelength. This relationship is fundamental in radio engineering, optics, and physics.
Common Frequency Examples
| Application | Frequency | Equivalent |
|---|---|---|
| Human Heart Rate | 1-2 Hz | 60-120 beats/min |
| AC Power (US) | 60 Hz | 60 cycles/sec |
| AC Power (Europe) | 50 Hz | 50 cycles/sec |
| AM Radio | 535-1,705 kHz | 0.535-1.705 MHz |
| FM Radio | 88-108 MHz | 88,000-108,000 kHz |
| Wi-Fi 2.4 GHz | 2,400 MHz | 2.4 GHz |
| CPU Clock Speed | 2-5 GHz | 2,000-5,000 MHz |
| Hard Drive (7,200 RPM) | 120 Hz | 7,200 RPM |
Frequently Asked Questions
- How do I convert hertz to kilohertz?
- To convert hertz (Hz) to kilohertz (kHz), divide by 1,000. To go from kHz to MHz, divide by 1,000 again. Each step (Hz → kHz → MHz → GHz) changes by a factor of 1,000.
- What is the frequency of common devices?
- Examples: heart rate ~1-2 Hz, AC power 50 Hz (many countries) or 60 Hz (US/Canada), AM radio ~535-1,705 kHz, FM radio ~88-108 MHz, Wi‑Fi ~2.4 GHz and 5 GHz, CPU clocks ~2-5+ GHz, visible light ~400-790 THz.
- How do I convert RPM to hertz?
- To convert RPM (revolutions per minute) to Hz (cycles per second), divide by 60. Example: 3,600 RPM ÷ 60 = 60 Hz. To convert Hz to RPM, multiply by 60.
- What is the relationship between frequency and wavelength?
- They’re inversely related: c = f × λ, where c is the speed of light, f is frequency, and λ is wavelength. Higher frequency means shorter wavelength.
- Why is AC power 60 Hz in the US but 50 Hz in Europe?
- The difference is historical standardization. Both frequencies work, but some equipment (especially motors and synchronous clocks) depends on the grid frequency, while many modern electronics can operate on both.
- What is CPU clock speed and why does it matter?
- Clock speed (GHz) is cycles per second. Higher isn’t always faster overall—core count, architecture, and workload matter—but it’s still a useful headline metric for performance.