Free Power Converter

Whether your task is converting horsepower to watts, translating kW to BTU/h, or exploring the fundamental definition of a watt, this online power converter provides a fast and reliable way to obtain cross-unit equivalents. With support for more than twenty distinct measurement units, simply enter a value in the unit you know, and the tool instantly updates all other fields.

Supported Power Units

The table below lists every unit integrated into the converter, along with its symbol and exact conversion factor to watts.

Unit	Symbol	Equivalent in Watts (W)
Watt	W	$1$
Picowatt	pW	$10^{-12}$
Nanowatt	nW	$10^{-9}$
Microwatt	µW	$10^{-6}$
Milliwatt	mW	$10^{-3}$
Kilowatt	kW	$10^{3}$
Megawatt	MW	$10^{6}$
Gigawatt	GW	$10^{9}$
Terawatt	TW	$10^{12}$
Petawatt	PW	$10^{15}$
BTU per hour	BTU/h	$0.293071$
Mechanical horsepower	hp(I)	$745.6998715823$
Metric horsepower	hp(M)	$735.49875$
Electric horsepower	hp(E)	$746$
Air horsepower	ahp	$745.69987158$
Boiler horsepower	hp(S)	$9812.5$
Kilocalorie per hour	kcal/h	$1.162222$
Kilocalorie per minute	kcal/min	$69.733333$
Erg per second	erg/s	$10^{-7}$
Ton of refrigeration	TR	$3516.8528420667$

The Watt Defined

The watt (W) is the SI unit of power, equivalent to one joule of energy transferred per second. In mechanical terms, one watt is exerted when a force of one newton moves an object at a constant velocity of one meter per second:

$$1\ \text{W} = 1\ \frac{\text{J}}{\text{s}} = 1\ \frac{\text{kg}\cdot\text{m}^2}{\text{s}^3}$$

From an electrical standpoint, power in watts is simply the product of voltage and current:

$$1\ \text{W} = 1\ \text{V} \times 1\ \text{A}$$

SI Prefixes for the Watt

The watt can be scaled across a wide range using standard SI prefixes. The following table lists these multiples together with typical applications.

Prefix	Symbol	Value	Common Applications
yocto	yW	$10^{-24}$	—
zepto	zW	$10^{-21}$	—
atto	aW	$10^{-18}$	Underwater sound pressure levels
femto	fW	$10^{-15}$	Radio receiver detection limits
pico	pW	$10^{-12}$	Radio astronomy, acoustics
nano	nW	$10^{-9}$	Radar receiver sensitivity
micro	µW	$10^{-6}$	Medical instruments (EEG, ECG)
milli	mW	$10^{-3}$	Laser pointers, hearing aids
centi	cW	$10^{-2}$	—
deci	dW	$10^{-1}$	—
—	W	$10^{0}$	Household bulbs, electronics
deca	daW	$10^{1}$	—
hecto	hW	$10^{2}$	—
kilo	kW	$10^{3}$	Motor ratings, industrial machines
mega	MW	$10^{6}$	Large motors, data centers, power plants
giga	GW	$10^{9}$	Power stations, grid generation
tera	TW	$10^{12}$	Global human energy consumption, lightning peaks
peta	PW	$10^{15}$	Solar energy reaching Earth's atmosphere, pulsed lasers
exa	EW	$10^{18}$	—
zetta	ZW	$10^{21}$	—
yotta	YW	$10^{24}$	—

Understanding Horsepower

James Watt originally created the horsepower unit in the 1700s to compare the output of his steam engines with draft horses. Over time, several distinct definitions emerged, five of which are included in this converter.

Mechanical Horsepower (hp(I)) ≈ 745.7 W
Based on Watt’s observation of a horse turning a mill wheel, this unit is defined as 33,000 foot‑pounds per minute. A horse can sustain about 2/3 hp over a working day and may briefly reach nearly 15 hp. For humans, sustained power is around 0.1 hp, while athletes such as Usain Bolt can momentarily generate over 3.5 hp.

Metric Horsepower (hp(M)) ≈ 735.5 W
Defined as the power needed to lift 75 kg one meter in one second against Earth’s gravity.

Electric Horsepower (hp(E)) = exactly 746 W
Commonly used for electric motors; this value is slightly above mechanical horsepower.

Air Horsepower (ahp) ≈ 745.7 W
Represents the ideal (100%‑efficient) power required to move a given airflow against a specified pressure. The formula is

$$\text{ahp} = \frac{\text{flow rate (CFM)} \times \text{pressure (in H}_2\text{O)}}{6,356}$$

and its watt equivalent matches mechanical horsepower.

Boiler Horsepower (hp(S)) ≈ 9,812.5 W
This unit refers to the energy needed to produce 34.5 pounds (15.65 kg) of steam per hour at zero gauge pressure and 212°F (100°C). Exact conversions may vary slightly by source; the tool uses 9,812.5 W.

Using the Power Converter

Performing a conversion is straightforward:

1. From the unit list, select the type you know (e.g., BTU/h, hp, kW, or any of the twenty units).
2. Enter the numerical value in the corresponding field.
3. The calculator automatically fills in the equivalent amounts for all other units.

For example, to find the wattage of a 10,000 BTU/h air conditioner, select “BTU/h,” type 10000, and read the result: 2,931 W. Converting an automobile engine rated at 200 hp yields about 149 kW. The tool can also be used to compare the power of different devices — for instance, see how your car’s horsepower stacks up against a household appliance.