Revolutions Per Minute to Millihertz (rpm to mHz)

1 revolution per minute equals 16.66666667 millihertz (rounded).

How to convert revolutions per minute to millihertz

To convert revolutions per minute to millihertz, multiply the number of revolutions per minute by 16.66666667. The factor is rounded to 10 significant digits. To go the other way, multiply millihertz by 0.06.

millihertz = revolutions per minute × 16.66666667

Example: 10 revolutions per minute = 166.6666667 millihertz.

About these units

Revolution Per Minute (rpm)

Metric (SI)Current unit

One 60th of a hertz. The unit for engine, motor and turntable speeds.

Records gave rpm its fame. The 78 rpm speed was not chosen for a clear engineering reason; Wikipedia says it apparently happened to be the speed of one of the early machines, and the Gramophone Company formally set it as a recording standard in 1912. Columbia unveiled the 33 and a third rpm LP on 21 June 1948, and RCA Victor released the 45 rpm single in February 1949, starting a period called the War of the Speeds.

One rpm equals one sixtieth of a hertz, so a disc at 60 rpm turns at 1 Hz. The SI does not recognise rpm as a unit, preferring hertz or radians per second, and r/min is the usual symbol in standards. Typical examples are a modern car engine idling at about 750 to 900 rpm, consumer hard drives at 7,500 to 10,000 rpm, power-generation turbines at 3,000 or 3,600 rpm, and uranium centrifuges of the Zippe type at 100,000 rpm or more.

1 revolution per minute = 0.01666666667 hertz (approximately).

Sources: Wikipedia: Revolutions per minute; Wikipedia: Phonograph record

Millihertz (mHz)

Metric (SI)Current unit

One thousandth of a hertz: one cycle every 1,000 seconds.

Millihertz describes oscillations so slow that a single cycle takes many seconds. One millihertz is 0.001 hertz, a period of 1,000 seconds, or about 16.7 minutes. At the other end of the scale, one revolution per minute works out to roughly 16.7 mHz, which is how a clock's second hand turns.

Slow phenomena are the natural home of the unit. The planned space-based gravitational-wave detector LISA is designed to operate from 0.1 to 10 mHz, a band that ground detectors cannot reach. The milli prefix is the SI factor of one thousandth, so a millihertz is a thousand times smaller than a hertz and a billion times smaller than a terahertz. Where signals are slower still, such as a daily cycle near 11.57 microhertz, microhertz take over.

1 millihertz = 0.001 hertz (exactly).

Sources: Wikipedia: Hertz; Wikipedia: Orders of magnitude (frequency); Wikipedia: Revolutions per minute

Related conversions

See all frequency units.