What’s the difference between HP, BHP and PS?

There’s not a more popular way to compare cars these days than a straight-up power figure. But there are so many different units are used for engine power that sometimes we can get lost.

What is Horsepower & Break Horsepower?

So, let me explain each of them and tell you which one we should all be using. Let’s start with horsepower and brake horsepower.

The standard unit used by the USA is horsepower originates from the birth of the steam engine. James Watt, the inventor of the steam engine. And he decided he wants to come up with the unit to compare his new engines to the horses of the time. That was dominating the haulage industry through experimentation. What decided that one horsepower was equal to a horse transporting 33,000 pounds of mass 1 foot in 1 minute. It is called Horsepower.

1 HP that equates to 746 Watts

We use this power unit to this day. To find the unit for horsepower, here is the equation.

To complicate things even further we use Brake Horsepower

That often clashes with the straight-up American horsepower. Brake horsepower is derived from the technique used to measure the power of a large drum with an internal water brake that measures the resisting braking force produced. 

When opposing the rotation of an engines’ crankshaft otherwise known as an old-school Dino or Brake horsepower

In America, This form of testing is undertaken with a few ancillary components attached to the engine. Allowing it to breathe more and transfer more energy.

In the UK however, we have all the ancillary components attached to the flight the air column power steering. This means that three horsepower values are slightly less than horsepower values across the board. Due to annoying but realistic losses. This often leads to confusion when translating engine power outputs across the Atlantic. 

PS the units for continental Europe.

The unit of choice for continental Europe is derived from the German word Pferdstarke that translates directly to Horsepower. 

PS is calculated in the same way as horsepower, apart from the whole thing is converted into metric units. That means instead of pounds and feet, we have kilograms and meters. 

1PS = 0.986hp

If, you are from France who uses the CV annotation, which means Cheval-Vapeur or steam horse. PS results now figure 1.4 percent higher than old-school horsepower. This is why manufacturers always lean towards using it.

And The kilowatt. 

The watt is calculated by using the other members of the metric system. 

  • The second 
  • The Joule 
  • The kilogram 
  • And the meter, used worldwide across all areas of engineering. 

The watt is a measure of energy transfer over time. And is the most simple way to measure power from an internal combustion engine. Because the numbers can get quite high. 

1kW = 1.341hp

The kilowatt is used, with 1 kilowatt equaling a 1000 watts. Like with horsepower, you can calculate engine power in kilowatts using the torque and engine speed divided by a constant. 


  • HP is the output horsepower rating of an engine, while BHP is the input brake horsepower of an engine.
  • BHP is the measurement of an engine’s power without any power losses, while HP is BHP less the power losses.
  • HP is measured by hooking up the engine to a dynamometer, while BHP is measured in a controlled environment without anything attached to the engine.

Leave a Reply

Your email address will not be published. Required fields are marked *