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Difference Between HP and BHP

horse-powerHP vs BHP

You are bound to have stumbled upon the term Horsepower, whether you own a vehicle or not. HP is a measurement which is used during ads for cars, and it’s also something that you will often hear being used by those who work in machine shops, or even men who are car enthusiasts, but what about the term Brake Horsepower, or BHP? The difference between the two is what we will now uncover.

First, let’s start with what HP is all about. Invented by James Watt, horsepower originally measured the amount of work, that a horse lifting coal out of a coal mine, could do in a minute. Back then, one HP equated to 33,000 foot-pounds. Today, you can easily convert HP into different units, like 1 HP that equates to 746 Watts. It can also be converted into British Thermal Units, or BTU, joules and calories.

However, the most common use of HP, as a unit, is to measure the power of an engine ‘“ which you can determine by hooking it to a dynamometer. What HP actually measures, is the maximum rate of acceleration and the top speed of the car.

On the other hand, Brake Horsepower measures the HP of an engine without considering the loss in power that is caused by some parts of the engine, like the generator, gearbox, water pump and other auxiliary parts.

There are actually no other key differences between BHP and HP, other than the fact that when BHP is measured, the engine torque is determined by applying a break to the flywheel ‘“ as opposed to using a torque converter, like in the case of HP.

To summerize, HP is measured with all the accoutrements attached to the engine, to determine its maximum rate and speed. BHP, on the other hand, is more of a theoretical calculation, which is made under lab-controlled conditions, and without having anything attached to the engine.

Summary:

1. HP is the output horsepower rating of an engine, while BHP is the input brake horsepower of an engine.

2. B HP is the measurement of an engine’s power without any power losses, while HP is BHP less the power losses.

3. 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.


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18 Comments

  1. I’d disagree with the descriptions used – much of it is closer in truth to the difference between gross power output and net power output.

    While the use of BHP to denote measurement at a load, or brake (not break, as spelled in the article) is correct, it does not necessarily mean that this must be at the engine flywheel – power as measured at the wheels by a dynomometer is also BHP, as it is still being measured at a brake.

    The article also omits certain erroneous uses of the term horsepower, such as the old British vehicle taxation system that rationalised HP as being related largely to cylinder bore in order to assign a levy – hence car models being known by numbers such as “seven” or “twelve”, denoting their taxable classification. Interestingly, this also had the side effect of encouraging manufacturers to build small-bore, long-stroke engines for a given capacity, to minimise the duty rate attracted.

  2. Dave is an idiot. Thanks for the article

  3. I agree with both Dave and Chris….both valid. I didn’t know about the taxation on the cylinder bores though. Ok so if I understand this correctly…BHP is in a controlled evnirnment with nothing attached to the engine except something such as a brake from an engine dyno, and the same can be said about “RWHP” rear wheel horse power……which is also considered a “break” or Brake lol ok now im confused again. All I do know is in the “real world” you loose power through the drive train= transmission, drive shafts, rear diffs, axles etc. these all play parts on “robbing” horse power or should I be more acurate and say Torque. Because the horse power is just the speed at which is turns…..not the force behind it kinda like volts vs amprage…….I do hear the term BHP and I have been in the auto industry for MANY years….in service depts and as a gear head growing up sooooo i need clarity here! lol

  4. When car manufactures advertise engine power these days, it isn’t BHP but HP. Or in other words net horsepower not gross horsepower.

  5. Whilst I applaud everyone for taking the trouble to contribute, the above exchanges are littered with techno-rubbish, and it is reasonably clear that none of the contributors have ever been directly involved in engine or vehicle performance measurements. I have, and rather than try to put everything straight here, I would recommend, to anyone interested, the Wikipedia article on Horsepower. Some may find the more technical content a little daunting, but I strongly recommend reading all the way through as there are answers there for almost everyone. (I confess I have not been through the Wikipedia article with a fine toothcomb, but on a speed-read it is dramatically more accurate than the stuff above.)
    BTW, Dave’s comments are basically correct. And Chris, that is NOT a maybe.

  6. Pls edit fine toothcomb to fine-tooth comb – I definitely do not comb my teeth.

  7. is bhp of a engine is greater than hp pls explian

  8. HP is LESS than BHP.

    Take the Bugatti Veyron, a much disputed example.

    Its BHP figure, before any losses, is 1001.

    Its HP figure, taking into account that the power must go through the gearbox etc is 987HP; If you were to apply the breaks at its top speed, they would only need to stop the power of 987BHP, because that is all that is being transferred to the road.
    That means 14BHP has been lost during the process of transferring power to the ground, meaning a 98.6% efficiency rating.

    Any questions? I hope not.

  9. Example of car: Bhp can be measured at the engine output and hp can be measured at wheel out put. (bhp-transmission loss =Hp).

  10. HP is called as Indicated Horse Power i.e.IHP means the Horsepower actually deveploped at the engine shaft. BHP means Brake horse power i.e. power actully used by the engine to perform the work. BHP is always less than IHP. IHP.-BHP.=FHP.FHP means power wasted in Engine friction.,it is also called as Frictional Horsepower.

  11. This article confuses more than it explains. A much simpler and arguably more accurate explanation would be:

    - HP = measured on the wheel, i.e. the power a vehicle will transfer to the road.

    - BHP = measured on the crankshaft, i.e. the power of the engine alone without any other components of a vehicle that “rob” the engine of power.

    One is a measure with everyday practicality. The other makes sense to engineers only, but is often used as a marketing gimmick to confuse the general public because it’s always higher.

    Neither measure the maximum rate of acceleration and are very different from torque, a measure that is thrown into this article for no good reason.

  12. “It can also be converted into British Thermal Units, or BTU, joules and calories.”

    uhhhhh, no.

    That’s like saying you could measure a cup of water in units of Niagara falls.

    No conversion can take away the time portion of a unit of power without defining time.

  13. Ok Mr Bugatti, knowing that no engine runs at 100% efficiency and considering that no self respecting company would sell a mode of transport that would have 1/2 hp to every bhp. My question is this, what is a reasonable % efficiency rating that I could use as a rule of thumb for figuring the hp or bhp when the other is given?
    And is there a slope involved that I could factor size of engine or other notable variables?
    Bottom line question- what is the formula for the hp and bhp?
    I’ll try google bhp-hp to see if I get anywhere.
    Ps: for those who want to correct me, my autocorrect already beat me up

  14. One very very important thing that has not been mentioned in this article is that horsepower has a different definition depending on where you are. A metric horsepower is 98.6% of the Imperial mechanical horsepower. I’m only mentioning this because the difference of bhp and hp is in the same category and sometimes car manufacturers use different definition of hp depending on where the engine came from.

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