Power is the measure of the rate at which work is done. The ability to correctly measure power was one of the main key factors that led to the industrial revolution. Power is a scalar quantity as it has no direction. The unit of power in the SI system is the joule per second (J/s) which is also known as the Watt (W) in honor of the Scottish mechanical engineer James Watt.

Units of Power

Watt     - W

Milliwatt    - mW

Kilowatt    - kW

Megawatt - mW

Gigawatt  - gW

How to measure power?

One watt is one joule of work done per second. So, this is the formula to measure power (P).

P=ΔE / Δt ,  where ΔE is the change in energy and Δt is the change in time.

Another unit of power is still widely used, and that’s the horsepower (hp). Since the 17th century, a metric horsepower has been considered as the power needed to lift 75 kg mass through a distance of 1 meter in 1 second. 

How many watts in a horsepower?

A mass acquires potential energy when being lifted against gravity, so we have 

Ep= m⋅g⋅h

Putting the numbers we have above, we get Ep= 735.5 W

How many horsepower is a horse?

The maximum output of a horse can be up to 15 horsepower and the maximum output of a human is just a bit above 1 single horsepower.

For more information, formulas and other conversions you can use our free Power Converter.