kWh to HP and HP to kWh Conversions

powerlines w150pxWhile HP is a unit of power, kWh is a unit of energy and direct conversion of these two units is not possible, without introducing the third parameter - time (T[s]).

kWh to HP and HP to kWh conversions are very important when both 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.

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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 unit and is exactly defined.

There are several definitions of HP, but the most used one define:

1 HP = 746 W

Since 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, energy given in kWh equals to system power output given in kilowatts, multipied by the time (given in seconds) the system was running:

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

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 to system power output given in horse power, multipied by the time (given in seconds) the system was running:

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

For short:

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

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

So, if You have value in HP/HPh, multiply it with 0.746 or divide it with 1.34 and You will get the equivalent value in kW (kilowatts)/kWh (kilowatthours) 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!


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

Effective output power of such 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

 


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:

HP to kWh

 

kWh to HP

HP:

Time (h):

kWh:

 

kWh:

Time (h):

HP:


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

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

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

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

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