Convert Hertz to RPM - Frequency Converter
This converter converts between frequency (hertz, Hz) and rotational speed (revolutions per minute, RPM). The direct mathematical relationship for pure unit conversion is fixed and lossless: 1 Hz equals 60 RPM.
Beyond the simple ratio, practical use cases include converting electrical frequency to motor synchronous speed (which depends on pole count), translating encoder pulse rates to RPM, and setting VFD or instrument setpoints. Where measurement accuracy matters, consult calibration practices and instrument limits.
The guidance and examples that follow reference recognized standards and technical resources from government laboratories and leading universities to support reliable results and safe application.
Interactive Converter
Convert between hertz and revolution per minute with precision rounding.
Quick reference table
| Hertz | Revolution per Minute |
|---|---|
| 1 Hz | 60 rpm |
| 5 Hz | 300 rpm |
| 10 Hz | 600 rpm |
| 25 Hz | 1,500 rpm |
| 50 Hz | 3,000 rpm |
| 100 Hz | 6,000 rpm |
Methodology
Direct unit conversion: multiply Hz by 60 to get RPM, divide RPM by 60 to get Hz. This is the canonical SI relationship and is exact for a single-cycle-per-revolution system.
Electric motors — synchronous speed: mechanical synchronous RPM depends on electrical frequency and the number of motor poles. Use the synchronous speed formula below and account for slip in induction motors when estimating actual running speed.
Encoders and pulse-based measurements: when a sensor emits multiple pulses per revolution, divide measured pulses-per-second by pulses-per-revolution, then multiply by 60 to get RPM. Follow instrument manufacturer calibration intervals and NIST guidance for traceability when accuracy is required.
Worked examples
1 Hz → 60 RPM (1 × 60 = 60).
50 Hz → 3000 RPM on a 2-pole synchronous shaft (120 × 50 ÷ 2 = 3000).
60 Hz → 3600 RPM on a 2-pole synchronous shaft (120 × 60 ÷ 2 = 3600).
Encoder example: 1000 pulses per second from a sensor with 20 pulses per revolution → RPM = (1000 ÷ 20) × 60 = 3000 RPM.
Expert Q&A
What is the exact relationship between hertz and RPM?
The exact SI relationship is RPM = Hz × 60. One hertz is one cycle per second; multiplying by 60 converts cycles per second to cycles per minute, which equals revolutions per minute for a one-cycle-per-revolution system.
How do I convert electrical frequency to motor RPM when pole count matters?
Use synchronous speed = (120 × f) ÷ P, where f is electrical frequency (Hz) and P is the motor pole count. For induction motors, actual running speed will be slightly lower due to slip; estimate actual speed as synchronous speed × (1 − slip).
Can I use Hz → RPM conversion for VFD setpoints?
Yes. For a simple shaft speed target, calculate the required electrical frequency from desired RPM (Hz = RPM ÷ 60 for a 2-pole motor equivalently using the synchronous formula with P). Always verify motor nameplate pole count and follow VFD manufacturer guidance and safety lockout procedures before applying changes.
How precise is the conversion? What about measurement uncertainty?
The mathematical conversion is exact, but practical precision depends on measurement instrument resolution, sampling rate, and calibration. Oscilloscopes, frequency counters, and encoders have defined uncertainties; follow NIST traceability and calibration intervals for measurements used in certification or safety-critical applications.
How do I convert pulses from an encoder to RPM?
Calculate revolutions per second as pulses per second divided by pulses per revolution, then multiply by 60 to get RPM. For noisy or aliasing-prone signals, use averaging or high-resolution timers and ensure sensor wiring and shielding meet manufacturer recommendations.
Are there safety or regulatory considerations when changing motor speeds?
Yes. Changing speed can affect torque, cooling, and connected machinery. Follow OSHA machine safety guidance, motor manufacturer recommendations, and applicable industry standards. For regulated environments or critical systems, consult qualified personnel and documented procedures before altering speeds.
Sources & citations
- NIST — International System of Units (SI) and unit definitions — https://www.nist.gov/pml/weights-and-measures/metric-si/si-units
- NIST — Calibration services and measurement traceability — https://www.nist.gov/calibrations
- U.S. Department of Energy — Electric Motor Systems and industrial efficiency guidance — https://www.energy.gov/eere/amo/industrial-efficiency-motor-systems
- OSHA — Machine guarding and machinery safety considerations — https://www.osha.gov/machine-guarding
- MIT OpenCourseWare — Rotational motion and angular frequency resources — https://ocw.mit.edu