To convert frequency to hertz, match the source unit to its SI relationship with Hz: divide by 1000 for every step up the SI ladder (kHz to Hz, MHz to kHz, GHz to MHz), divide rad/s by 2π to get Hz, and divide rpm or BPM by 60 to get Hz. The hertz is the SI unit for one complete cycle per second, and every other frequency unit in common use is either an SI-prefixed scale of the hertz or a per-minute rate that must be normalized to seconds. Going the other way — converting a frequency from hertz into kHz, MHz, GHz, THz, rad/s, rpm, or BPM — uses the same factors in reverse: multiply by 1000 for each step up the ladder, multiply by 2π for rad/s, and multiply by 60 for rpm or BPM. The arithmetic is straightforward once the relationships are clear, but mistakes around angular frequency and per-minute rates are common because the direction of the conversion is easy to flip. The fastest way to get an exact answer is to type the number, pick the source and target units, and read the result with the Frequency Converter, which routes every pair of units through hertz internally.
Before converting anything, it helps to know exactly what the hertz measures. The hertz, abbreviated Hz, is the SI unit for frequency and equals exactly one complete cycle per second. The unit honors Heinrich Hertz, who confirmed the existence of electromagnetic waves in the late 1880s. Any time a signal repeats — a sound wave, an alternating current, a clock tick — its frequency is the count of those repeats per second, expressed in hertz.
The Hertz Unit and the SI Prefix Ladder
SI prefixes scale the hertz up and down by powers of ten. According to the BIPM, the standard prefixes used in frequency work follow a clean factor-of-1000 pattern, which is why converting between neighboring units is a simple matter of moving the decimal point three places:
- 1 kilohertz (kHz) = 10³ Hz = 1,000 Hz
- 1 megahertz (MHz) = 10⁶ Hz = 1,000,000 Hz
- 1 gigahertz (GHz) = 10⁹ Hz = 1,000,000,000 Hz
- 1 terahertz (THz) = 10¹² Hz = 1,000,000,000,000 Hz
- 1 millihertz (mHz) = 10⁻³ Hz = 0.001 Hz
Because each step on this ladder is exactly a factor of 1000, converting hz to khz just means dividing by 1000 — 2,500 Hz becomes 2.5 kHz — and going khz to mhz or mhz to ghz follows the same rule. The reverse direction multiplies by 1000 per step, so 1 GHz works out to 1,000 MHz, 1,000,000 kHz, and 1,000,000,000 Hz in a single chain. Millihertz runs the other way at one-thousandth of a hertz, useful for very slow oscillations like tidal cycles or seismic drift where the period stretches into many seconds per cycle.
Converting with the Frequency Converter
Using a calculator removes the need to memorize every scaling factor, and the same three inputs cover every supported pair of units:
- Type the frequency you want to convert into the value field of the Frequency Converter.
- Choose the source unit from the "From" dropdown — Hz, kHz, MHz, GHz, THz, mHz, rpm, BPM, rad/s, or deg/s.
- Choose the target unit from the "To" dropdown.
- Read the converted result immediately.
- Tick "Show all units at once" to display every unit from millihertz to terahertz alongside rpm, BPM, rad/s, and deg/s in a single view.
Because every conversion routes through hertz, the SI unit for one cycle per second, any pair of units stays exact and consistent in both directions. Entering 1 GHz and switching from GHz to Hz produces 1,000,000,000; switching back returns exactly 1 with no rounding loss along the way.
Common Frequency Units Compared
The table below summarizes the verified relationship between each supported unit and the hertz. Values follow the BIPM SI prefix definitions and the standard identities 1 rad/s = 1/(2π) Hz, 1 deg/s = 1/360 Hz, and 1 rpm = 1 BPM = 1/60 Hz.
| Unit | Symbol | Relationship to 1 Hz | Typical use |
|---|---|---|---|
| Hertz | Hz | 1 Hz = 1 cycle per second | Audio tones, mains power |
| Kilohertz | kHz | 1 kHz = 1,000 Hz | AM radio, audio bands |
| Megahertz | MHz | 1 MHz = 1,000,000 Hz | FM radio, CPU clocks |
| Gigahertz | GHz | 1 GHz = 1,000,000,000 Hz | Wi-Fi, processors, cellular bands |
| Terahertz | THz | 1 THz = 1,000,000,000,000 Hz | Spectroscopy, photonics |
| Millihertz | mHz | 1 mHz = 0.001 Hz | Slow oscillations, tides |
| Revolutions per minute | rpm | 1 rpm = 1/60 Hz | Motors, hard drives, fans |
| Beats per minute | BPM | 1 BPM = 1/60 Hz | Music tempo, heart rate |
| Radians per second | rad/s | 1 rad/s ≈ 0.159155 Hz | Angular frequency, signals |
| Degrees per second | deg/s | 1 deg/s = 1/360 Hz | Servo rates, robotics |
Each row above describes an exact relationship defined by an SI prefix or a published identity, so any value from the calculator matches the table to full precision.
Angular Frequency and the 2π Relationship
Angular frequency, written ω (omega), describes how fast something rotates in radians per second rather than cycles per second. Because one complete cycle sweeps a full 2π radians, the two quantities are linked by the identity ω = 2π × f. This identity produces two clean conversions:
- 1 Hz = 2π rad/s ≈ 6.283185 rad/s
- 1 rad/s = 1/(2π) Hz ≈ 0.159155 Hz
The direction of the conversion is what trips people up most often. A value in rad/s is roughly 6.28 times larger than the same frequency written in Hz, which means 1 rad/s actually describes a smaller frequency than 1 Hz. Going from Hz to rad/s multiplies by 2π; going from rad/s to Hz divides by 2π. Using 2π exactly rather than the rounded 6.2832 keeps the conversion round-trip clean: 50 Hz becomes 100π rad/s, and dividing by 2π returns exactly 50 Hz with no rounding loss.
Worked example: 50 Hz in rad/s
Take a 50 Hz mains signal — the kind used across much of Europe and Asia. To express it as angular frequency, substitute f = 50 into ω = 2π × f:
ω = 2π × 50 = 100π ≈ 314.159 rad/s
To verify, divide the result back by 2π: 314.159 / (2π) = 50 Hz. The same identity works in reverse: if a wheel is rotating at 314.159 rad/s, its frequency in Hz is 314.159 / (2π) = 50 Hz.
rpm and BPM: Per-Minute Rates Normalized to Seconds
Revolutions per minute (rpm) and beats per minute (BPM) both count events per minute instead of per second, so each equals exactly 1/60 Hz. The math is identical, but the labels describe different worlds: rpm belongs to spinning hardware like motors, fans, and hard drives, while BPM describes musical tempo or heart rate. Keeping them as separate labels in the converter avoids accidental confusion between a 128 BPM drum track and a 128 rpm spindle.
- 60 rpm = 1 Hz, so 3000 rpm = 50 Hz — a common induction-motor speed under 50 Hz mains.
- 120 BPM = 2 Hz, so a resting human heart at 60 BPM = 1 Hz.
- To convert rpm or BPM to Hz, divide by 60; to convert Hz to rpm or BPM, multiply by 60.
Because the math is identical, the same factor handles both directions. A track labeled 128 BPM converts to roughly 2.133 Hz (128 ÷ 60), and 2.133 Hz converts back to exactly 128 BPM when multiplied by 60. The labels carry the meaning; the underlying numbers do not change.
Where Frequency Conversions Actually Matter
Frequency conversions show up across nearly every technical field, and the unit on hand usually depends on the scale of the phenomenon being measured. In audio and music, audible tones live in Hz while song tempo is expressed in BPM, so a 120 BPM metronome is exactly 2 Hz. In radio and wireless, AM radio sits in kHz, FM radio and television in MHz, and modern Wi-Fi, Bluetooth, and cellular bands in GHz. Processors and digital timing circuits quote clock speeds in MHz or GHz that often need to be cross-checked against the underlying Hz for signal-integrity work. Light and spectroscopy deal with even higher frequencies, with visible light sitting in the hundreds of THz and infrared and ultraviolet on either side. Rotating machinery like motors, hard drives, and propellers is usually specified in rpm, which must be divided by 60 to compare against an Hz reference.
Because the same physical phenomenon shows up under different labels depending on the field, a tool that holds every relationship consistently is more reliable than re-doing the arithmetic by hand at the bench. Once the value is in hertz, the next step for photonics and spectroscopy work is often to convert that frequency into photon energy using the Planck relation — see the frequency-to-energy guide for that calculation. The Frequency Converter keeps each unit label separate while routing every conversion through hertz internally, so the round-trip math stays exact in either direction. Everything runs client-side in your browser, so values never leave the device.