;Attowatt: The sound intensity in water corresponding to the international standard reference
sound pressure of 1
μPa is approximately 0.65 aW/m2. ;Femtowatt: Powers measured in femtowatts are typically found in references to
radio and
radar receivers. For example, meaningful
FM tuner performance figures for sensitivity, quieting and
signal-to-noise require that the
RF energy applied to the antenna input be specified. These input levels are often stated in dBf (
decibels referenced to 1 femtowatt). This is 0.2739 microvolts across a 75-ohm load or 0.5477 microvolt across a 300-ohm load; the specification takes into account the RF
input impedance of the tuner. ;Picowatt: Powers measured in picowatts are typically used in reference to radio and radar receivers,
acoustics and in the science of
radio astronomy. One picowatt is the international standard reference value of
sound power when this quantity is expressed in decibels. ;Nanowatt: Powers measured in nanowatts are also typically used in reference to radio and radar receivers. ;Microwatt: Powers measured in microwatts are typically stated in
medical instrumentation systems such as the
electroencephalograph (EEG) and the
electrocardiograph (ECG), in a wide variety of scientific and engineering instruments, and in reference to radio and radar receivers. Compact
solar cells for devices such as
calculators and
watches are typically measured in microwatts. ;Milliwatt: A typical
laser pointer outputs about five milliwatts of light power, whereas a typical
hearing aid uses less than one milliwatt.
Audio signals and other electronic signal levels are often measured in
dBm, referenced to one milliwatt. ;Watt: PC
power supply units are typically specified in watts; modern
graphics cards usually have
TDPs of a few hundred watts. ;Kilowatt :The kilowatt is typically used to express the output power of
engines and the power of
electric motors, tools, machines, and heaters. It is also a common unit used to express the
electromagnetic power output of broadcast radio and television
transmitters. One kilowatt is approximately equal to 1.34
horsepower. A small electric heater with one
heating element can use 1 kilowatt. The average
electric power consumption of a household in the United States is about 1 kilowatt. A surface area of 1 square meter on Earth receives typically about one kilowatt of sunlight from the Sun (the
solar irradiance) (on a clear day at midday, close to the equator). ;Megawatt: Many events or machines produce or sustain the conversion of energy on this scale, including large electric motors; large warships such as aircraft carriers, cruisers, and submarines; large
server farms or
data centers; and some scientific research equipment, such as
supercolliders, and the output pulses of very large lasers. A large residential or commercial building may use several megawatts in electric power and heat. On railways, modern high-powered
electric locomotives typically have a peak power output of , while some produce much more. The
Eurostar e300, for example, uses more than , while heavy
diesel–electric locomotives typically produce and use . U.S.
nuclear power plants have net summer capacities between about . The earliest citing of the megawatt in the
Oxford English Dictionary (
OED) is a reference in the 1900
''Webster's International Dictionary of the English Language. The OED
also states that megawatt
appeared in a November 28, 1947, article in the journal Science'' (506:2). video explaining gigawatts ;Gigawatt: A gigawatt is typical annually averaged power consumption for a city of 1.8 million habitants, and is the output of a large power station. The gigawatt is thus used for large power plants,
power grids, and, increasingly, large data centers. For example, by the end of 2010, power shortages in China's Shanxi province were expected to increase to 5–6 GW and the installation capacity of wind power in Germany was 25.8 GW. The largest unit (out of four) of the Belgian
Doel Nuclear Power Station has a peak output of 1.04 GW.
HVDC converters have been built with power ratings of up to 2 GW. ;Terawatt: The
primary energy used by humans worldwide was about 160,000 terawatt-hours in 2019, corresponding to an average continuous power consumption of 18 TW that year.
Earth itself emits 47±2 TW, far less than the energy received from solar radiation. The most powerful lasers from the mid-1960s to the mid-1990s produced power in terawatts, but only for
nanosecond intervals. The average lightning strike peaks at 1 TW, but these strikes only last for 30
microseconds. ;Petawatt: A petawatt can be produced by the current generation of lasers for time scales on the order of picoseconds. One such laser is
Lawrence Livermore's
Nova laser, which achieved a power output of 1.25 PW by a process called
chirped pulse amplification. The duration of the pulse was roughly 0.5
ps, giving a total energy of 600 J. Another example is the Laser for Fast Ignition Experiments (LFEX) at the Institute of Laser Engineering (ILE),
Osaka University, which achieved a power output of 2 PW for a duration of approximately 1
ps. Based on the average total solar irradiance of 1.361 kW/m2, the total power of sunlight striking Earth's atmosphere is estimated at 174 PW. The planet's average rate of global warming, measured as
Earth's energy imbalance, reached about 0.5 PW (0.3% of incident solar power) by 2019. ;Yottawatt: The power output of the Sun is 382.8 YW, about 2 billion times the power estimated to reach Earth's atmosphere. == Conventions in the electric power industry == In the
electric power industry,
megawatt electrical (
MWe or MWe) refers by convention to the
electric power produced by a generator, while
megawatt thermal or
thermal megawatt (MWt, MWt, or MWth, MWth) refers to
thermal power produced by the plant and
megawatt mechanical (MWm) to
mechanical power. For example, the
Embalse nuclear power plant in Argentina uses a
fission reactor to generate 2,109 MWt (i.e. heat), which creates steam to drive a turbine, which generates 648 MWe (i.e. electricity). Other
SI prefixes are sometimes used, for example
gigawatt electrical (GWe). The
International Bureau of Weights and Measures, which maintains the SI-standard, states that further information about a quantity should not be attached to the unit symbol but instead to the quantity symbol (e.g., rather than ) and so these unit symbols are non-SI. In compliance with SI, the energy company
Ørsted A/S uses the unit megawatt for produced electrical power and the equivalent unit
megajoule per second for delivered heating power in a
combined heat and power station such as
Avedøre Power Station. When describing
alternating current (AC) electricity, another distinction is made between the watt and the
volt-ampere. While these units are equivalent for simple
resistive circuits, they differ when loads exhibit
electrical reactance. ==Radio transmission==