What is Hertz (Hz) to RPM Frequency Converter?
Hz to RPM, motor speed This tool runs entirely in your browser. No data is sent to any server, and no signup is needed.
Hertz to Rpm Converter
Hz to RPM converter
Multiply by 60 to convert Hz to RPM.
How is this calculated?
1 Hz = 60 RPM. Conversion factor sourced from NIST SP 811 (Guide for the Use of the International System of Units).
Hertz (Hz) to RPM: 1 Hz = 60 RPM. Used for motor speed, audio frequencies, AC power.
About this converter
Hertz (Hz) is the SI unit of frequency: one cycle per second. Revolutions per minute (RPM) is the same quantity expressed per minute. Because a minute is exactly 60 seconds, 1 Hz = 60 RPM and 1 RPM = 1/60 Hz exactly. The conversion is dimensional and has no decimals.
How it works
Both units describe rotational or oscillation frequency. The hertz is named after Heinrich Hertz (BIPM SI Brochure, Table 4: 1 Hz = 1 s-1). RPM is cycles per minute. The conversion just rescales the time base:
1 Hz = 1 cycle / 1 s
= 60 cycles / 60 s
= 60 cycles / 1 min
= 60 RPM
1 RPM = 1 / 60 Hz
= 0.01666666... Hz
Synchronous motor speed (RPM)
N = 120 x f / p
where f = line frequency (Hz), p = number of poles
For pure conversion, multiply Hz by 60 to get RPM; divide RPM by 60 to get Hz. The factor 60 is exact (BIPM definition of the minute).
Worked example
An engineer needs to size a variable-frequency drive (VFD) for a 4-pole induction motor that should run at 1,500 RPM under load. What line frequency should the VFD output, assuming 4 percent slip?
- Target shaft speed: 1,500 RPM = 1,500 / 60 = 25 Hz mechanical rotation.
- Convert to synchronous speed accounting for slip: N_sync = 1,500 / (1 - 0.04) = 1,563 RPM.
- For a 4-pole motor, line frequency f = N_sync x p / 120 = 1,563 x 4 / 120 = 52.1 Hz.
- Set the VFD output to 52 Hz; the motor will run at ~1,500 RPM (25 Hz at the shaft).
- Sanity check: at the standard 60 Hz line frequency, the same 4-pole motor would run at 60 x 120 / 4 = 1,800 RPM synchronous and ~1,728 RPM with slip.
Reference table
| Hz | RPM | Typical machine |
|---|---|---|
| 0.5 Hz | 30 RPM | Slow rotating display |
| 12 Hz | 700 RPM | Car engine idle |
| 25 Hz | 1,500 RPM | Slow-speed pump |
| 30 Hz | 1,800 RPM | 4-pole 60 Hz motor |
| 50 Hz | 3,000 RPM | 2-pole 50 Hz EU motor |
| 60 Hz | 3,600 RPM | 2-pole 60 Hz US motor |
| 120 Hz | 7,200 RPM | 7,200 RPM hard drive |
| 250 Hz | 15,000 RPM | Formula 1 V6 engine |
| 1,000 Hz | 60,000 RPM | Turbocharger turbine |
| 5,000 Hz | 300,000 RPM | Dental high-speed drill |
Common pitfalls
- Hz is not always rotational. Hertz applies to any periodic phenomenon: sound waves (20 to 20,000 Hz), AC mains (50 or 60 Hz), CPU clocks (gigahertz). RPM only applies to actually rotating shafts. A 4 GHz CPU does NOT spin at 240,000,000,000 RPM; it switches logic states 4 billion times per second.
- AC frequency vs motor RPM. Mains is 50 Hz in Europe, 60 Hz in the US. A 2-pole synchronous motor runs at 3,000 RPM at 50 Hz; the same motor runs at 3,600 RPM at 60 Hz. Plugging a 60 Hz motor into 50 Hz lowers its speed by 17 percent and changes torque characteristics.
- Synchronous vs actual RPM (slip). Induction motors run 3 to 5 percent below synchronous speed because the rotor lags the field. A "1,800 RPM" 4-pole motor in datasheets really runs 1,710 to 1,750 RPM under nominal load.
- RPM vs angular velocity (rad/s). RPM is cycles per minute; angular velocity omega = 2 pi x f rad/s. Bearing engineers use rad/s; HVAC engineers use RPM. To convert RPM to rad/s, multiply by 2 pi / 60 = 0.10472.
- Hertz, rpm, and the human hearing range. The audible range is 20 to 20,000 Hz. A subwoofer at 30 Hz would have to vibrate 1,800 RPM if it were a spinning shaft. Mixing audio frequency and motor RPM in datasheets creates confusion.
Related tools and references
Frequently asked questions
What is the exact Hz to RPM conversion?
Hertz is cycles per second; RPM is revolutions per minute. Because there are exactly 60 seconds in a minute, 1 Hz = 60 RPM and 1 RPM = 1/60 Hz = 0.01666... Hz. The factor 60 is exact, not approximate. The hertz is the SI unit of frequency, equal to one cycle per second (BIPM SI Brochure, Table 4).
Why is US mains power 60 Hz and Europe 50 Hz?
In the late 1880s Westinghouse standardised on 60 Hz in the US after experiments with arc lamps and rotary converters; AEG in Germany picked 50 Hz to align with metric base-60 thinking. A 60 Hz two-pole synchronous motor runs at 3,600 RPM; a 50 Hz one at 3,000 RPM. Both standards persist because rewiring entire national grids is uneconomic.
How are AC frequency and motor RPM related?
Synchronous AC motor RPM = 120 x line frequency / number of poles. A 60 Hz 4-pole motor runs at 120 x 60 / 4 = 1,800 RPM synchronous. Induction motors run slightly slower due to slip (typically 3 to 5 percent). So a 60 Hz 4-pole induction motor runs at 1,710 to 1,750 RPM under load.
How fast do everyday rotating machines spin in Hz and RPM?
Hard-drive platter 5,400 RPM (90 Hz) or 7,200 RPM (120 Hz). Car engine idle ~700 RPM (~12 Hz), redline 6,000 to 8,000 RPM (100 to 133 Hz). Formula 1 engines hit 15,000 RPM (250 Hz). Aircraft jet turbine fan 5,000 to 10,000 RPM. Electric drill 0 to 2,500 RPM. Dental drill 200,000 to 400,000 RPM (3,300 to 6,700 Hz).
Sources
- BIPM (2019) The International System of Units (SI), 9th edition, Table 4, definition of the hertz.
- NIST Special Publication 811 (2008) Guide for the Use of the International System of Units.
- IEC 60050 International Electrotechnical Vocabulary, rotating machinery terminology.
- NEMA MG 1 Motors and Generators, induction motor slip and synchronous speed.