Battery Equivalents and Replacements

kWh to HP and HP to kWh Conversions

While HP is a unit of power, kWh is a unit of energy, and direct conversion of these two units is impossible without introducing the third parameter - time (T[s]).

kWh to HP and HP to kWh conversions are very important when both the power and energy of internal combustion engines are transferred, stored, and compared with the energy and power of electric motors, inverters, pumps, winches, and other similar units that are powered by electric energy.

Updated: February 14, 2024.


Conversion Formulas - How to Convert kWh to HP and HP to kWh?

As said before, HP is the unit of power, while kWh is the unit of energy.

As a power unit, the 'HP' (Horse Power) has a long history that is beyond the scope of this article (and this site) - it is enough to say that the unit was used to measure the strength of a horse (hence the name) and to compare it with the strength of early steam engines.

Today, HP as a unit is mostly used for describing/rating the strength or power of various engines (internal combustion engines, steam turbines, and similar) - even power generators provide the generator output power in watts, but also often provide the strength of its engine in HPs.

On the other hand, 'Watt' is an SI (International System of Units) unit and is exactly defined.

There are several definitions of HP, including:

Mechanic or hydraulic horsepower (HP): one mechanic or hydraulic horsepower equals 745.699872 W or 0.745699872 kW:

1 HPI = 745.699872 W = 0.745699872 kW

Electrical horsepower (HP): one electrical horsepower equals exactly 746 W or 0.746 kilowatts:

1 HPE = 746 W = 0.746 kW

Metric horsepower (HP): one metric horsepower equals 735.49875 W or 0.73549875 kilowatts:

1 HPM = 735.49875 W = 0.73549875 kW

There are other HP definitions, including tax horsepower, drawbar horsepower, boiler horsepower, etc., but the most used one is electrical horsepower, which defines:

1 HP = 746 W

Since the SI prefix 'kilo' (shortened to 'k') means thousand (or 103), it also means that:

1 HP = 746 W = 0.746 kW

Likewise:

1 kW = 1/0.746 HP = 1.34048 HP ≈ 1.34 HP

As a measure of energy, kWh (kilo-Watt-hour) equals to:

1 kWh = 1000 W * 3600 s = 3.6 * 106 J = 3.6 MJ (Mega-Joules)

Generally, the energy given in kWh equals the system power output given in kilowatts, multiplied by the time (given in seconds) the system was running, divided by 3600 (number of seconds in one hour):

E (kWh) = P(kW) * T(s) / 3600

Similarly, one horsepower-hour (HPh) equals to:

1 HPh = 1 HP * 3600 s = 746 W * 3600 s = 2685600 J = ~2.7 MJ = 0.746 kWh

Again, the energy given in HPh equals the system power output given in horsepower, multiplied by the time (given in seconds) the system was running divided by 3600 (again, number of seconds in one hour):

E (HPh) = P(HP) * T(s) / 3600

For short:

1 HP = 0.746 kW → P (kW) = 0.746 * P (HP); E(kWh) = 0.746 * E(HPh)

1 kW = 1.34 HP → P (HP) = 1.34 * P (kW); E(HPh) = 1.34 * E(kWh)

So, if You have a value in HP/HPh, multiply it by 0.746 or divide it by 1.34, and You will get the equivalent value in kW (kilowatts)/kWh (kilowatt-hours) and vice versa.

E(kWh) = 0.746 * P(HP) * T(h)

In most situations, a calculator app on the computer or smartphone can do the job, but sometimes a common or preferably 'scientific' calculator can come in very handy!


kWh to HP and HP to kWh Conversion Calculator

In order to convert HP to kWh and kWh to HP, feel free to use this conversion calculator - write the value that You have and click 'Calculate' to convert it (Note: we are assuming electric horsepower 1HP = 0.746kW):

HP to kWh

HP:

Time (h):

kWh:

 

kWh to HP

kWh:

Time (h):

HP:


kwh to hp w600px

Conversion Example

Here is a very simple conversion example that provides insight into how these conversions are done and how easy they can be:

If a generator features a 10 HP engine with a built-in inverter that features 85% efficiency, how much energy given in kWh can that generator provide in 3 hours?

10 HP engine equals:

P(kW) = 0.746 * P(HP) = 7.46 kW

The effective output power of such a power generator is:

P(kW-eff) = P(kW) * 0.85 = 7.46 kW * 0.85 = 6.341 kW

Thus, if the output power of the generator is 6.341 kW, that generator during three hours of operation provides:

E(kWh) = 6.341 kW * 3 h = 19.023 kWh = ~19 kWh


Long Story Short: Unit conversions, including HP to kW and back, are easy; just be sure to remember the right formulas:

1 HP = 0.746 kW → P (kW) = 0.746 * P (HP); E(kWh) = 0.746 * E(HPh)

1 kW = 1.34 HP → P (HP) = 1.34 * P (kW); E(HPh) = 1.34 * E(kWh)

E(kWh) = 0.746 * P(HP) * T(h)

And don't forget to use the calculator, especially for larger values.