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How to convert kilowatts to horsepower?


Horsepower is a unit of power. It is approximately equal to the value of 75 kgf / m / s., Which corresponds to the effort that must be expended to lift the load of 75 kg. to a height of one meter in one second.

What is 1 horsepower equal to? If we take any encyclopedia and look at what horse power is, then we will read that it is an off-system unit of power measurement that is not used in Russia. Although on any site of dealership dealerships, engine power is indicated in horsepower.

What is this unit, what is it equal to?

Speaking of engine horsepower, most of us present a simple picture: if you take a herd of 80 horses and a car with an engine power of 80 hp, then their forces will be equal and no one will be able to pull the rope.

If you try to recreate this situation in real life, then the herd of horses will win, because in order for the engine to develop such power, it needs to spin the crankshaft to a certain number of revolutions per minute. Horses rush from the spot and drag the car behind them, thus breaking the gearbox.

In addition, you need to understand that horsepower is a standard unit of power, while each horse is individual and some individuals can be much stronger than others.

Horsepower was introduced into circulation back in 1789. The famous inventor James Watt wanted to demonstrate how much more profitable to use steam engines, rather than horses to do the job. He simply took and calculated how much energy the horse spends so that with the simplest lifting mechanism - wheels with ropes fixed on it - to pull coal barrels out of the shaft or pump out water using a pump.

It turned out that one horse can pull a load weighing 75 kilograms at a speed of 1 m / s. If you translate this power into watts, it turns out that 1 hp is 735 watts. The power of modern cars is measured in kilowatts, respectively 1 hp. = 0.74 kW.

To convince the owners of the mine to switch from horsepower to steam, Watt proposed a simple way: measure what work the horses can do in a day, and then connect the steam engine and calculate how many horses he can replace. It is clear that the steam engine was more profitable, because it was able to replace a certain number of horses. The owners of the mine realized that it was cheaper to maintain a car than an entire stable with all the ensuing consequences: hay, oats, manure and so on.

It is also worth saying that Watt incorrectly calculated the strength of one horse. Only very strong animals can lift a weight of 75 kg at a speed of 1 m / s, in addition, they will not be able to work for a long time in such conditions. Although there is evidence that for a short time one horse can develop power up to 9 kW (9 / 0.74 kW = 12.16 hp).

Kinds of horsepower

  • Metric horsepower equal to a lift of 75 kg per second per 1 meter. It is applied in Europe
  • Mechanical horsepower equal to 745.7. very rarely used as a unit of measure in English-speaking countries
  • Electric horsepower equal to 746 watts., sometimes indicated by the plates of electric motors.
  • Boiler horsepower equal to 1000 kgf · m / s. or 9.8 kW or 33,475 Btu / hour. (unit used in the USA)
  • Hydraulic horsepower equal to 745.7 watts.

How engine power is determined

At the moment, the easiest way to measure the real power of the engine is with a dyno stand. The car is driven to a stand, it is firmly fixed, then the driver accelerates the engine to maximum speed and the real power in hp is displayed on the board. Permissible error - +/- 0.1 hp As practice shows, it often turns out that the nameplate power does not correspond to the real one, and this can indicate the presence of a wide variety of malfunctions - from poor-quality fuel, to a drop in compression in the cylinders.

It is worth saying that due to the fact that horsepower is a non-systemic unit, it is calculated differently in different countries. In the USA and England, for example, one hp It is 745 watts, and not 735 as in Russia.

Be that as it may, but everyone has become accustomed to this particular unit of measurement, since it is convenient and simple. In addition hp used in calculating the cost of CTP and CASCO.

Agree, if you read in the characteristics of the car - engine power is 150 hp. - it’s easier for you to orient yourself on what he is capable of. A record of 110.33 kW is not enough to say. Although convert kilowatts to hp quite simply: we divide 110.33 kW by 0.74 kW, we get the desired 150 hp

I would also like to remind you that the concept of “engine power” is not very indicative in itself, other parameters must also be taken into account: maximum torque, revolutions per minute, car weight. It is known that diesel engines are low-speed and maximum power is achieved at 1500-2500 rpm, while gasoline accelerates longer, but at better distances show better results.

How to convert horsepower to kW

There are several options for the mutual translation of these units:

  1. Online calculators. The easiest and fastest way. Requires constant access to the Internet.
  2. Match tables. They contain the most common values ​​and are always at hand.
  3. Translation Formulas. Knowing the exact correspondence of units, you can quickly transfer one number to another and vice versa.

In practice, the following numerical values ​​are used:

  • 1 liter with. = 0.735 kW,
  • 1 kW = 1.36 liters. with.

Most often, the second correspondence is used: it is easier to work with numbers greater than one. To carry out the calculations, the kW index is multiplied by this coefficient. The calculation in this case looks like this:

88 kW x 1.36 = 119.68 = 120 liters. with.

Why exactly 0.735 kW

1 liter with. approximately equal to the value of 75 kgf / m / s - this is an indicator of the effort required to lift a load weighing 75 kg to a height of 1 m in 1 second. Different countries use different types of this unit with different values:

  • metric = 0.735 kW (used in Europe, used in the standard conversion from kW to hp),
  • mechanical = 0.7457 kW (previously used in England and English-speaking countries, almost out of use),
  • electric = 0.746 kW (used for marking electric motors),
  • boiler room = 9.8 kW (used in the USA in energy and industry),
  • hydraulic = 0.7457.

In Russia, a European, called metric horsepower equal to 0.735 kW is used. It is formally phased out, but continues to be used in the calculation of taxes.

Practical aspect

The value of the transport tax in Russia depends on engine power. In this case, l are taken for the unit of account. c.: the tax rate is multiplied by their number. The number of payment categories varies by region. For example, in Moscow, 8 categories are determined for cars (prices are valid for 2018):

  • up to 100 liters with. = 12 rub.,
  • 101-125 l. with. = 25 rub.,
  • 126-150 l. with. = 35 rub.,
  • 151-175 l. with. = 45 rubles.,
  • 176-200 l. with. = 50 rub.,
  • 201-225 l. with. = 65 rub.,
  • 226-250 l. with. = 75 rub.,
  • from 251 liters with. = 150 rub.

The price is for 1 liter. with. Accordingly, with a power of 132 liters. with. the car owner will pay 132 x 35 = 4620 rubles. in year.

Earlier in the UK, France, Belgium, Spain, Germany, vehicle tax depended on the number of “horses”. With the introduction of kilowatts in some countries (France) they abandoned l. with. completely in favor of the new universal unit, in others (Great Britain), the size of the car was taken into account as the basis of the transport tax. In the Russian Federation, the tradition of using the old unit of measure is still respected.

In addition to calculating the transport tax, in Russia this unit is used for motor third party liability insurance (CTP): in calculating the premium for compulsory insurance of vehicle owners.

Another practical application, now of a technical nature, is the calculation of the actual engine power of a car. When measuring, the terms gross and net are used. Gross measurements are carried out at the stand without taking into account the operation of related systems - a generator, a cooling system pump, etc. The gross value is always higher, but does not show the power produced under normal conditions. If the kilowatts indicated in the documents are translated in l. with. In this way, only the amount of engine operation can be estimated.

For an accurate assessment of the power of the mechanism, this is impractical, because the error will be 10-25%. In this case, the actual engine performance will be overestimated, and when calculating the transport tax and compulsory motor liability insurance, the prices will be increased, since each unit of power is paid.

The net measurement at the stand is aimed at analyzing the operation of the machine under normal conditions, with all auxiliary systems. The net value is less, but more accurately reflects power in normal conditions with the influence of all systems.

A dynamometer, a device connected to the engine, will help to more accurately measure power. It creates a load on the engine and measures the amount of energy produced by the engine against the load. Some car services offer the use of dynamometer stands (dynostands) for such measurements.

Also, power can be measured independently, but with some error. By connecting the laptop cable to the car and running a special application, you can fix the engine power in kW or hp at different speeds. The advantage of this option is that the program will display the calculation error immediately after the control evaluation, and also immediately convert from kilowatts to horsepower, if the measurement was carried out in SI units.

Non-systemic units are gradually becoming a thing of the past. Power values ​​are increasingly indicated in watts. However, while horsepower is used, there will be a need for its conversion.

KW to horsepower ratio

Horsepower (hp) is an off-system unit of power that appeared around 1789 with the advent of steam engines. Inventor James Watt coined the term “horsepower” to illustrate how economically more profitable his machines are in manpower. Watt concluded that, on average, a horse lifts 180 pounds per 181 feet per minute. Rounding off the calculations in pound-feet per minute, he decided that the horsepower would be equal to 33,000 of these same pound-feet per minute. Of course, the calculations were taken for a long period of time, because for a short time a horse can "develop" a power of about 1000 kgf · m / s, which is approximately equal to 13 horsepower. They call such power - boiler horsepower.

There are several units in the world called horsepower. In European countries, Russia and the CIS, as a rule, horsepower refers to the so-called "metric horsepower", equal to about 735 watts (75 kgf · m / s).

In the automotive industry, the UK and the USA most often horsepower. equate to 746 watts, which is 1.014 metric horsepower. Also in the US industry and energy, electric horsepower (746 W) and boiler horsepower (9809.5 W) are used.


The force multiplied by the shoulder of its application, which the engine can give out to overcome certain resistance to movement. Determines the speed at which the motor reaches its maximum power. The calculated formula for torque from engine displacement:

Micr = VHxPE / 0.12566where

  • VH - engine displacement (l),
  • PE is the average effective pressure in the combustion chamber (bar).

Engine speed

Crankshaft rotation speed.

The formula for calculating the power of an internal combustion engine of a car is as follows:

P = Mcr * n / 9549 [kW]where:

  • Mcr - engine torque (Nm),
  • n - crankshaft revolutions (rpm),
  • 9549 - coefficient, in order to substitute revolutions in rpm, and not by alpha cosines.

Since, according to the formula, we get the result for kW, if necessary, you can also convert it to horsepower or simply multiply by a factor of 1.36.

Using these formulas is the easiest way to convert torque into power.

And in order not to go into all these details, a quick calculation of the internal combustion engine power online can be done using our calculator.

But, unfortunately, this formula only reflects the effective power of the motor, which does not all reach exactly the wheels of the car. After all, there are losses in the transmission, transfer case, to parasitic consumers (air conditioning, generator, power steering, etc.) and this does not take into account such forces as rolling resistance, lifting resistance, aerodynamic resistance.

How to calculate power by engine capacity

If you do not know the engine torque of your car, then to determine its power in kilowatts, you can also use a formula of the following type:

Ne = Vh * pe * n / 120 (kW) where:

  • Vh - engine displacement, cm³
  • n - rotational speed, rpm
  • pe is the average effective pressure, MPa (on conventional gasoline engines it leaves about 0.82 - 0.85 MPa, forced - 0.9 MPa, and for a diesel engine from 0.9 and 2.5 MPa, respectively).

To get the power of the engine in “horses”, and not kilowatts, the result should be divided by 0.735.

Calculation of engine power by air flow

The same approximate calculation of engine power can be determined by air flow. The function of such a calculation is available to those who have an on-board computer installed, since it is necessary to fix the value of the flow when the car engine, in third gear, spins up to 5.5 thousand revolutions. The resulting value with DMRV is divided by 3 and we get the result.

The formula how to calculate the power of the engine for air flow in the end looks like this:

Such a calculation, like the previous one, shows the gross power (bench test of the engine without taking into account losses), which is 10–20% higher than the actual one. And also it is worth considering that the readings of the DMRV sensor strongly depend on its contamination and calibrations.

Calculation of power by mass and acceleration time to hundreds

Another interesting way to calculate the engine power for any type of fuel, whether gasoline, diesel or gas, is based on acceleration dynamics. To do this, using the weight of the car (including the pilot) and the acceleration time to 100 km. And so that the power calculation formula is as close as possible to the truth, you must also take into account the slip loss, depending on the type of drive and the speed of reaction of different gearboxes. Approximate start-up losses for front-wheel drive will be 0.5 seconds. and 0.3-0.4 in rear-wheel drive cars.

Using this engine power calculator, which will help determine the engine power based on the dynamics of acceleration and mass, you can quickly and accurately determine the power of your iron horse without going into technical specifications.

Calculation of ICE power by nozzle performance

An equally effective indicator of the power of an automobile engine is the performance of injectors. Previously, we considered its calculation and the relationship, therefore, it will not be difficult to calculate the amount of horsepower by the formula. The estimated power is calculated according to the following scheme:

Where, the load factor is not more than 75-80% (0.75 ... 0.8) the composition of the mixture at maximum productivity is somewhere around 12.5 (enriched), and the BSFC coefficient will depend on what kind of engine you have, atmospheric or turbocharged (atmosphere - 0.4-0.52, for turbo - 0.6-0.75).

Having learned all the necessary data, enter the indicators in the appropriate cells of the calculator and by clicking the "Calculate" button you will immediately get a result that will show the real engine power of your car with a slight error. Note that you do not need to know all the parameters presented, you can clear the power of the internal combustion engine using a single method.

The value of the functionality of this calculator is not in calculating the power of a stock car, but if your car has undergone tuning and its mass and power have undergone some changes.

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