Hertz to Millihertz (Hz to mHz)

1 hertz equals 1,000 millihertz exactly.

How to convert hertz to millihertz

To convert hertz to millihertz, multiply the number of hertz by 1,000. This factor is exact. To go the other way, multiply millihertz by 0.001.

millihertz = hertz × 1,000

Example: 10 hertz = 10,000 millihertz.

About these units

Hertz (Hz)

Metric (SI)Current unit

The SI unit of frequency: one cycle per second. Named after Heinrich Hertz.

Heinrich Rudolf Hertz (1857 to 1894) was a German physicist who, in experiments between 1886 and 1889, produced and detected radio waves with a spark-gap transmitter and a loop receiver. He showed that they travel at the speed of light and can be polarised, reflected and refracted, confirming Maxwell's theory. Asked about uses for them, he is said to have replied, Nothing, I guess. The International Electrotechnical Commission established the name hertz in 1935, and the CGPM adopted it in 1960, replacing cycles per second.

One hertz is one cycle per second, equal to s to the minus one. A clock ticking once a second runs at 1 Hz, a human heart at rest beats at around 1.2 Hz, and young ears hear roughly 20 Hz to 20,000 Hz. The SI treats cycle itself as not a unit, and the hertz applies only to periodic events, whereas the becquerel counts random radioactive decays, even though both are one per second. The second is now defined by fixing the caesium frequency at exactly 9,192,631,770 hertz.

The hertz is the reference unit for frequency on this site.

Sources: Wikipedia: Hertz; Wikipedia: Heinrich Hertz; BIPM: SI Brochure, 9th edition

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.