Millihertz (mHz) - Unit Information & Conversion

Quick Answer

What is a Millihertz? A millihertz (mHz) equals 0.001 Hz or one cycle per 1,000 seconds (approximately 16.67 minutes). Used for ultra-slow oscillations like tidal forces, seismic activity, Earth's oscillations, and some astronomical measurements. 1 mHz = 0.001 Hz = 1 cycle per 1000 seconds. Use our frequency converter for instant conversions.

Key Facts: Millihertz

Property	Value
Symbol	mHz
Quantity	Frequency
System	Metric/SI Derived
Derived from	Hertz
Category	Frequency
Standard Body	NIST / ISO

Definition

1 mHz = 0.001 Hz = 1/1000 Hz = 1 cycle per 1,000 seconds ≈ 1 cycle per 16.67 minutes

Millihertz in Context

Understanding extremely slow oscillations:

• 1 Hz = 1 cycle per second (normal audio)
• 0.1 Hz = 1 cycle per 10 seconds (slow swing)
• 0.01 Hz = 1 cycle per 100 seconds (very slow)
• 0.001 Hz (1 mHz) = 1 cycle per 1,000 seconds (ultra-rare)
• Relationship: 1 mHz × 1,000 = 1 Hz

Common Uses

Seismology: Ultra-low frequency seismic waves and Earth oscillations (0.3-10 mHz) - critical for understanding deep Earth structure. Geophysics: Tidal deformations, Earth's free oscillations after major earthquakes, core-mantle interaction. Astronomy: Stellar oscillations, Sun's vibration modes, solar physics. Oceanography: Ultra-long period ocean waves, tsunami frequencies, global tidal analysis.

Real-World Examples

Seismic Oscillations (Earthquakes & Earth Resonance)

Earth's natural vibrations operate in the millihertz range:

Event/Mode	Frequency	Period	Duration	Significance
Chandler wobble	0.00001 mHz	14 months	Long-term	Earth's axis drift
Earth's nutation	0.00003 mHz	18.6 years	Long-term	Moon's orbital influence
Earth normal modes	0.3-5 mHz	3-55 minutes	After quakes	Deep Earth resonance
0S mode	0.325 mHz	51 minutes	Fundamental	Entire Earth oscillates
Rayleigh waves	0.5-2 mHz	8-30 minutes	Seismic	Surface waves from quakes
Love waves	0.5-2 mHz	8-30 minutes	Seismic	Horizontal surface waves
Free oscillations	0.3-3 mHz	5-55 minutes	Post-earthquake	Earth "ringing" for hours

Measurement context: 2011 Tohoku (Japan) earthquake caused Earth to oscillate at 0.324 mHz for days

Solar and Stellar Oscillations

Sun and stars vibrate at millihertz frequencies:

Source	Typical Frequency	Period	Application
Solar p-modes	1-2 mHz	8-16 minutes	Sun's surface convection
Solar g-modes	0.1-1 mHz	16-160 minutes	Sun's interior structure
Solar 5-minute oscillation	3.3 mHz	5 minutes	Acoustic waves
Red giant stars	0.2-1 mHz	15-80 minutes	Stellar structure probe
White dwarf oscillations	1-2 mHz	8-16 minutes	Cooling star study

Scientific use: Helioseismology uses solar oscillations to map the Sun's interior

Ocean and Tidal Frequencies

Large-scale ocean phenomena:

Phenomenon	Frequency	Period	Wavelength/Cycle
Tsunami	0.001-0.01 mHz	100-10,000 seconds	Long-wavelength
Seiche (bay oscillation)	0.01-0.1 mHz	100-10,000 seconds	Bay-dependent
Kelvin waves	0.01-0.1 mHz	100-10,000 seconds	Equatorial
Inertial oscillation	0.01-0.1 mHz	100-10,000 seconds	Latitude-dependent
Diurnal tide	0.041 mHz	24 hours	Moon-Sun pull
Semi-diurnal tide	0.083 mHz	12 hours	Twice-daily

Comparing Time Periods

How long is one cycle at different frequencies?

Frequency	Period	Cycles in 1 Hour	Cycles in 1 Day	Real-World Parallel
1 Hz	1 second	3,600	86,400	Audio tone
0.1 Hz	10 seconds	360	8,640	Pendulum swing
0.01 Hz	100 seconds	36	864	Slow wave
1 mHz	1,000 seconds (16.7 min)	3.6	86.4	Very slow oscillation
0.1 mHz	10,000 seconds (2.8 hours)	0.36	8.6	Extremely slow
0.01 mHz	100,000 seconds (27.8 hours)	0.036	0.86	Nearly daily

Insight: At 1 mHz, something completes 86 full cycles in a full day

How do I convert mHz to Hz?

Formula: Hz = mHz ÷ 1,000

Examples:

• 1 mHz = 0.001 Hz
• 100 mHz = 0.1 Hz
• 1,000 mHz = 1 Hz

Reverse: mHz = Hz × 1,000

mHz to Hz converter →

What is 1 mHz in time period?

1 mHz = 1 cycle per 1,000 seconds

Period = 1/frequency:

• 1 mHz = 1,000 seconds = 16 minutes 40 seconds
• 0.1 mHz = 10,000 seconds = 2 hours 46 minutes
• 10 mHz = 100 seconds = 1 minute 40 seconds

When are millihertz measurements used?

Millihertz is used for phenomena that cycle very slowly:

Seismic Science:

• Earth's normal modes: 0.3-5 mHz
• Ultra-long seismic waves

Geophysics:

• Earth tides
• Core-mantle coupling

Space Science:

• Spacecraft trajectory corrections
• Some satellite orbital perturbations

Most everyday frequencies are measured in Hz or higher (kHz, MHz, GHz).

mHz to Hz converter →