Power Converter
If you are wondering how to convert horsepower to watts or watts to calories, this power converter is a tool for you. Change quickly between twenty different power units by typing one value into the calculator. If you are curious about power conversion factors, BTU to watts conversion, or you just want to know what a watt actually is, keep scrolling, and you'll find the answer.
You can also check out our dbm to watts calculator to learn how to convert between decibels per milliwatt (dBm) and watts.
Power units
In this power converter, we implemented twenty popular force units. The most common ones are the SI unit watt and its nine most frequently used multiples:
 picowatts (pW)
 nanowatts (nW)
 microwatts (µW)
 milliwatts (mW)
 kilowatts (kW)
 megawatts (MW)
 gigawatts (GW)
 terawatts (TW)
 petawatts (PW)
And also ten other power units, including 5 types of horsepower units:
 British thermal units per hour (Btu/h, sometimes known as Btu or BTU)
 Mechanical horsepowers (hp(l))
 Metric horsepowers (hp(M))
 Electric horsepowers (hp(E))
 Air horsepower (ahp)
 Boiler horsepowers (hp(S))
 kilocalories per hour (kcal/h)
 kilocalories per minute (kcal/min)
 ergs per second (erg/s)
 ton of refrigeration (TR)
Power conversions
The formulas implemented in our power converter to change between any from 11 popular power units into watts look as follows:

1 picowatt [pW] = 0.000000000001 watt [W] = 10⁻¹² watt [W]

1 nanowatt [nW] = 0.000000001 watt [W] = 10⁻⁹ watt [W]

1 microwatt [µW] = 0.000001 watt [W] = 10⁻⁶ watt [W]

1 milliwatt [mW] = 0.001 watt [W] = 10⁻³ watt [W]

1 kilowatt [kW] = 1000 watt [W] = 10³ watt [W]

1 megawatt [MW] = 1000000 watt [W] = 10⁶ watt [W]

1 gigawatt [GW] = 1000000000 watt [W] = 10⁹ watt [W]

1 terawatt [TW] = 1000000000000 watt [W] = 10¹² watt [W]

1 petawatt [PW] = 1000000000000000 watt [W] = 10¹⁵ watt [W]

1 Btu/hour [Btu/h] = 0.293071 watt [W]

1 mechanical horsepower [hp(l)] = 745.6998715823 watt [W]

1 metric horsepower [hp(M)] = 735.49875 watt [W]

1 electric horsepower [hp(E)] = 746 watt [W]

1 air horsepower [ahp] = 745.69987158 watt [W]

1 boiler horsepower [hp(S)] = 9812.5 watt [W]

1 kilocalorie/hour [kcal/h] = 1.162222 watt [W]

1 kilocalorie/minute [kcal/min] = 69.733333 watt [W]

1 erg/second [erg/s] = 10⁻⁷ watt [W]

1 ton of refrigeration [TR] = 3516.8528420667 watt [W]
What is a watt?
The watt is a basic SI unit of power and is equal to one joule per second.
The basic definition of a watt unit looks as follows:
If an object's velocity is held constant at one meter per second against a constant opposing force of one newton, the rate at which work is done is 1 watt.
1 watt = 1 joules / second
1 W = 1 × J / s = 1 × N × m / s = 1 × kg × m² / s³
in basic SI units
The watt can also be defined in terms of electromagnetism – electric power is the rate at which electrical work is performed when a current of one ampere flows across an electrical potential difference of one volt.
1 watt = 1 ampere × 1 volt
To calculate the relationship between the real, reactive, and apparent power in an AC circuit, check out this power factor calculator.
SI multiples for watt (W)
What's the relationship between a watt and, e.g., a megawatt? Or how much power is 1 Gigawatt? The table below presents the basic SI multiples for watt and their applications.
Value  SI symbol  Name  Applications 

10⁻²⁴ W  yW  yoctowatt  
10⁻²¹ W  zW  zeptowatt  
10⁻¹⁸ W  aW  attowatt  sound intensity in water 
10⁻¹⁵ W  fW  femtowatt  radio and radar receivers 
10⁻¹² W  pW  picowatt  radio and radar receivers, acoustics, radio astronomy 
10⁻⁹ W  nW  nanowatt  radio and radar receivers 
10⁻⁶ W  µW  microwatt  radio and radar receivers, medical instrumentation systems (EEG, ECG) 
10⁻³ W  mW  milliwatt  acoustics (dBm), hearing aids, laser pointers 
10⁻2 W  cW  centiwatt  
10⁻¹ W  dW  deciwatt  
1 W  W  watt  bulbs 💡, different electronic devices 
10¹ W  daW  decawatt  
10² W  hW  hectowatt  
10³ W  kW  kilowatt  different electronic devices, engines, motors, tools, machines, heaters, broadcast radio, television transmitters 
10⁶ W  MW  megawatt  large electric motors (e.g., cruisers, submarines), server clusters, supercolliders, power plants 
10⁹ W  GW  gigawatt  large power plants or power grids 
10¹² W  TW  terawatt  total power used by humans worldwide, average lightning strike peaks at 1 TW 
10¹⁵ W  PW  petawatt  total power of sunlight striking Earth's atmosphere, current generation of lasers (but for order of picoseconds) 
10¹⁸ W  EW  exawatt  
10²¹ W  ZW  zettawatt  
10²⁴ W  YW  yottawatt 
Horsepower 🐎 and its types
The unit was introduced in the 18th century to compare steam engines with the power of draft horses. Later it was expanded to different types of new engines and machines. The most often used units are mechanical and metric horsepower, equal to ~745.7 watts and ~735.5 watts, respectively.
1. (Imperial) mechanical horsepower
A mechanical horsepower was defined by James Watt to be equal to precisely 33,000 ft lbf/min. Watt found this value by an estimation of horse performance – he observed how many times a horse could turn a mill wheel with a given diameter, then he assumed the force with which the horse pulled and rounded the obtained value to get the final 33,000 ft lbf/min.
Thus, the horse work rate is about one hp in sustained activity (but it's instead a maximum value, the average horse can sustain 2/3 hp for a working day
, ), in contrast to a possible peak power of almost 15 hp. For a standard healthy human, these values are equal to about 1.2 hp (0.89 kW) of peak and 0.1 hp of sustained work. Athletes such as, e.g., Usain Bolt can even produce 3.5 hp (2.6 kW) for a short time.2. Metric horsepower
One metric horsepower is defined as the power needed to raise a mass of 75 kilograms against the Earth's gravitational force over a distance of one meter in one second.
3. Electric horsepower
Slightly higher value than mechanical horsepower, the electrical equivalent is equal to exactly 746 watts.
4. Air horsepower
It's the horsepower required to move a given volume of air against given pressure, assuming 100% efficiency. It may be used in air conditioning, heating, and ventilating systems.
ahp = flow rate (cubic feet / minute) × pressure (inches water column) / 6,356
Air horsepower is equal in value to mechanical horsepower and hydraulic horsepower.
5. Boiler horsepower
Boiler horsepower (hp(S), also abbreviated as bhp or BHP) is usually defined as the amount of energy required to produce 34.5 pounds (15.65 kg) of steam per hour at a pressure of 0 psig (0 bar) and temperature of 212 °F (100 °C).
It was used in the USA, Australia, and New Zealand, but the formula differed among these countries. In our power conversion tool, we assumed 1 boiler horsepower = 9,812.5 W. However, you may find values such as 9810.55407 W, 9809.5 W, or 9809 W in some sources.
Power converter – how to use
Assume you want to convert BTU to watts to find the power of your heating or cooling system in watts.

Select the unit you want to convert. In our case, it's Btu/h (sometimes abbreviated as just Btu or BTU).

Enter the value into the right box. If it's not visible, click on the power unit name in the appropriate section to select the unit from a dropdown list. Let's say that we have a 10,000 BTU air conditioner.

Here it is! The power converter displays our value in different units, including watts. So we found out that 10,000 Btu/h is equal to 2,931 watts.
Now it's your turn to try this power converter yourself! For example, compare car engine performance 🚗 with another device (why not the vacuum cleaner?) by changing the car's horsepower to watts.