⚙️

RPM to Hz Converter

Convert rotational speed in revolutions per minute (RPM) to shaft frequency in hertz (Hz = RPM / 60) and angular velocity (rad/s = RPM × 2π / 60), and back again. A live 1X–10X harmonic-order table shows the multiples of running speed you would look for in a vibration spectrum, each annotated with its typical diagnostic meaning.

ℹ The conversions here are exact arithmetic — Hz = RPM/60 is simply a unit change. The order→fault notes (1X imbalance, 2X misalignment, ½X oil whirl, etc.) are common diagnostic conventions, not guarantees or a diagnosis: the same order can have several causes, and confirming one needs a calibrated accelerometer, phase data and machine context. This tool tells you which frequencies to look for; it does not measure vibration or judge severity. Verify your running speed (a slipping induction motor turns slightly below its synchronous speed).

Enter a speed or frequency

Type in any one box — the others update instantly. Use the presets for common motor and mains-tied speeds.

Presets:

Harmonic orders (1X–10X of running speed)

Each order is a whole-number (or simple-fraction) multiple of the shaft frequency above. The “typically” column lists the most commonly cited meaning of energy at that order — a starting point for diagnosis, never a verdict.

How It Works

A rotating shaft completes some number of revolutions per minute (RPM). Frequency in hertz (Hz) counts cycles per second, and one revolution is one cycle, so the conversion is just a change of time base: divide by the 60 seconds in a minute. Hz = RPM / 60, and inversely RPM = Hz × 60. At 1800 RPM a shaft turns 30 times a second, i.e. 30 Hz. This shaft frequency is the running speed or 1X order of the machine.

Angular velocity measures the same rotation in radians per second. One full turn is 2π radians, so ω = RPM × 2π / 60 = 2π × Hz. Engineers use ω (rad/s) in dynamics, control and resonance equations; technicians use RPM on the nameplate; vibration analysts use Hz and orders on the spectrum. This converter keeps all three in lock-step so you can move between the worlds in one place.

In vibration analysis the running speed sets a comb of orders — integer multiples 1X, 2X, 3X… and a few sub-synchronous fractions like ½X. Because faults excite characteristic orders, knowing the exact 1X–10X frequencies in Hz tells you where on the spectrum to look. The mapping in the table (1X often imbalance, 2X often misalignment, harmonics with looseness, sub-1X with oil whirl) reflects long-standing field conventions, but these are diagnostic clues, not certainties: one order can arise from several causes, and a real diagnosis needs amplitude from a calibrated accelerometer, phase relationships, the spectrum shape, and knowledge of the machine. Use these frequencies as targets, then confirm with measurement.

Frequently Asked Questions

How do I convert RPM to Hz?
Divide the RPM by 60, because there are 60 seconds in a minute and one revolution equals one cycle. So Hz = RPM / 60: 1800 RPM is 30 Hz, 3600 RPM is 60 Hz. To go the other way, multiply hertz by 60 (RPM = Hz × 60). This is exact unit arithmetic, not an estimate.
What is the rad/s (angular velocity) result?
Angular velocity ω expresses the same rotation in radians per second. One revolution is 2π radians, so ω = RPM × 2π / 60, which is also 2π × frequency in Hz. It is the form used in dynamics, control systems and resonance formulas; 1800 RPM equals about 188.50 rad/s.
What does the 1X / 2X / 3X order table mean?
An "order" is a multiple of the running speed (1X = shaft frequency, 2X = twice it, and so on), the natural grid a vibration spectrum is read against. The notes are common conventions: 1X commonly relates to imbalance, 2X to misalignment, multiple harmonics to mechanical looseness, and sub-synchronous components below 1X to oil whirl or rub. They point you to the frequency to inspect — they are not a diagnosis on their own.
Does a peak at 1X always mean imbalance?
No. 1X is the single most common signature of mass imbalance, but a bent shaft, a soft foot, certain misalignments and even resonance near running speed can also raise 1X. Confirming imbalance needs phase measurements (a steady phase that follows the rotor) and amplitude from a calibrated sensor — the order alone is a clue, not proof.
Why might my motor not run at exactly 1800 or 3600 RPM?
Those are the synchronous speeds of AC induction motors (120 × line frequency ÷ poles). Under load an induction motor slips a little below synchronous speed — a "1800 RPM" motor often runs at roughly 1750 RPM. Use the actual measured speed for accurate order frequencies; the presets give the synchronous reference, not the loaded running speed.
Can this tool measure my machine's vibration?
No. It is a converter and a frequency map, not a measurement. It tells you which frequencies correspond to each order so you can search for them in a spectrum, but it does not capture vibration, give amplitude in mm/s or g, or assess severity. For real measurement use a calibrated accelerometer and analyzer; for severity see ISO 10816, which requires a calibrated instrument.

Related Tools

Angular Frequency Calculator
ω, f and period in one place (rad/s ↔ Hz).
Hz to BPM Converter
Cycles per second to beats per minute.
Period to Frequency Converter
Seconds per cycle ↔ Hz.
Bearing Fault Frequency Calculator
BPFO, BPFI, BSF and FTF from running speed.
Fan Blade Pass Frequency Calculator
Blade-pass frequency = blades × shaft Hz.
Gear Mesh Frequency Calculator
GMF = teeth × shaft Hz, plus sidebands.
← All Vibration & Mechanical Tools