Convert kilowatts to horsepower: how many drugs in one kW + principles and calculation methods

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Lydia Korzheva
Last update: November 2019

Horsepower and Watt. The first term is a power meter, which is becoming increasingly obsolete, gradually being supplanted from electrical engineering, the second is modern. Motorists, however, resist, preferring visibility.

Sometimes it is required to translate “l. with." in watts - let's see how they compare.

What is horsepower?

The only measure of power the equivalent of which is recognized worldwide is kilowatts. Despite this, where there are internal combustion engines, their strength is indicated in horsepower. This unit is also popular in calculating the transport tax.

For this reason, owners of their own vehicles have to transfer kilowatts to this off-system unit.

The expression has firmly entered the vocabulary ever since when James Watt from Scotland in the late 17th century introduced the first steam engine to replace horse-drawn traction.

New unit
Horsepower, as a term, a meter, allowed the average person to visualize how many horses are being replaced by a machine

An interesting fact: at one time in France, or rather, in Paris, there were norms for the draft effort of crews (omnibuses).

According to them, a horse harnessed to the crew, for a working day of 5 and a half hours and a draft force of 25.8 kg, should run 55,056 km daily. The power developed by horses was 72 kgm / s.

French power unit
The power value in France is almost identical to that received in England. The French unit was called Cheval vapeur. In literal translation, it sounds like a "steam horse"

Observing the work of the horse lifting the load from the mine, he found that at a constant speed of 1 m / s it lifts a load weighing close to 75 kg.

By calculation, James Watt defined horsepower as the power at which a horse’s luggage weighing 250 kg can lift 30 cm in 1 s. Therefore, 1 hp = 75 kgm / s, and if in watts, then - 735.499 watts.

Following this, the following horsepower options came into use:

  • electric;
  • mechanical;
  • indicator;
  • boiler rooms and many others.

Since the definition of horsepower is ambiguous in order to put things in order in this matter, in 1882 the English Association of Engineers at its congress approved a previously unknown unit of measure for power. It was named in honor of the inventor - W (watt) or W, and it became international.

Later, the adoption of SI prescribed designate the engine power in kilowatts. The unit began to be used in technical documentation, in advertising booklets. To put an end to the obsolete concept, in 2010 the EU Directive prohibited the use of horsepower without dubbing in kilowatts.

Benefits of Using Machines
When James Watt drove the concept of horsepower, he simply sought to show the benefits of using cars instead of animals. He did this by calculating the cost of energy that a horse and mechanism spend on lifting a load

Different types of horsepower are associated with watts as follows:

  • electric - 746 W;
  • mechanical - 745,699871582 W;
  • metric - 735.4988 W;
  • indicator - 745.6998715822 W;
  • boiler room - 9809.5 watts.

European countries mainly use metric horsepower. By it is meant the power used to lift up weights of 75 kg at the same speed and generally accepted acceleration g = 9.80665 m / s².

In the United States and the United Kingdom, in the automotive industry, horsepower is 1.0138696789 metric hp. or 745.6998815 watts. Boiler, electric hp also used in America.

Moving cargo
While the metric unit is 0.74 kW, when determining this unit in feet and pounds, it is associated with the movement of goods weighing 1 pound per 33,000 feet in 1 minute or 1 pound in a distance of 550 feet in 1 second

The unit “horsepower” has been removed from the official turnover in Russia. When calculating the transport tax, the metric version of the hp still applied. In this case, the tax value is multiplied by the number of hp.

Watt and Kilowatt Units

A watt power unit is included in the SI system. One watt is 1 J work done in 1 second.

This measure of power can also be expressed through the ratio of other units:

  1. Newton moved 1 m in 1 s.
  2. One kilogram displaced within 1 m.
  3. Volt-ampere

One kilowatt contains 1000 watts. Using this unit, the energy of sound, heat, current power, radiation fluxes is measured.

Ways to convert kilowatts to l. with.

The mutual transition of these two units can be accomplished by several methods:

  1. Online convectors. There are software products for this, but you need access to the network. If there is Internet, then the method is very fast and simple.
  2. Tables. They contain values ​​that are more common than others.
  3. Formulas for translation. Used to “convert” physical quantities manually.

Numerical values ​​used in practice: 1 kW = 1.36 hp, 1 hp = 0.735 kW. It’s easier to work with the first expression, and to simplify, 1.36 is rounded to 1.4. In this case, the error is small and if we estimate the power approximately, then its value can be neglected.

Ways to determine power
The way in which the power was determined in fact affects the amount of power received when transferring from one value to another

Practically converting kW to hp will have the following form:

90 kW x 1.4 = 126 hp and reverse: 140 hp : 1.4 = 100 kW.

For more accurate calculations in order to determine how much horsepower is in a kilowatt, a coefficient of 1.35962162 is used.

Horsepower in a car

The value in kW divided by 0.735 is the horsepower in the car. It is comparable to the action performed in 1 s in order to lift a 75 kg load by 1 m. At the same time, gravity is taken into account.

The greater the engine power of the car in relation to the mass of the vehicle, the more efficient it is. In other words, the less the body weighs, the greater the power indicator and the greater the acceleration of the car.

Determination of power in hp
In order to convert the nameplate power of a particular car from kilowatts to horsepower, it is necessary to divide the existing value by 0.735

For example, the Jeep Wrangler has a power of 177 hp. and a gross weight of 2.505 tons. The ratio of power to full weight will be: 177: 2505 = 70.56. Acceleration to hundreds of kilometers per hour - 10.1 s.

If you take a powerful Ferrari 355 F1 car with a 375 hp engine. and weighing 2.9 tons, the ratio will be 375: 2900 = 0.129. Acceleration to 100 km / h - 4.6 seconds.

Conversion table kW to hp
This is a table with which you can very easily convert horsepower to kilowatts without any calculation

The designation of horsepower in different countries is not the same. While in Russia it is hp, then in English-speaking countries - hp, in the Netherlands - pk, in Germany - PS, in France - CV.

When the kilowatt was introduced, in France they stopped using CVs and completely switched over when calculating the tax on these new units of power. In the UK, the dimensions of the car were taken as the basis for the tax on the vehicle.

In Russia, in addition to the transport tax, hp used in calculating the size of the payment for insurance of the iron "horse" (CTP). Apply hp and in determining the actual power of a motor vehicle. At the same time, terms such as gross and net are in use.

The first indicator is measured at the stand and the operation of the cooling pump, generator and other related systems is not taken into account. Its value is always higher than the second parameter, but does not reflect the power generated in normal circumstances.

If you use this method to transfer the kilowatts indicated in the passport, then only the amount of motor operation will be established. To accurately evaluate its power, using this method is impractical due to the large error, which is equal to from 10 to 25%. Since the performance of the motor will be overestimated, the transport tax will also be large.

The stand gives out the net value taking into account auxiliary systems. The parameter obtained in this way corresponds more precisely to power under normal conditions. Even more accurately determine the power can such a device as a dynamometer.

Capacity tax
The more horsepower an engine has in a car, the higher the tax must be paid to the owner of the vehicle, so every motorist must be able to convert power from kW to hp. and vice versa

From how much horsepower the car’s engine accelerates, the car’s coolness and its dynamic characteristics depend.

If the car does not have technical documentation, and its power must be known, you can do this in two ways.

# 1: Method for determining vehicle power

To determine power in traditional horsepower using this option, values ​​such as torque, engine speed are needed. You can find them in the instructions or on the Internet, if you specify the appropriate brand of car.

Further, the found parameters are multiplied. For the calculation, the following expression is used:

(RPM x T) / 5252 = HP

It RPM - engine speed, T - the moment of torsion, 5.252 - the number of radians per second. So, one of the models of the Hyundai Santa Fe car has a torque of 227 at a speed of 4000, so 227 x 4000 = 908 000. The result is divided by 5252 and horsepower is obtained:

908,000: 5252 = 173 bhp

# 2: Power calculation method

On a car engine, voltage in volts, amperage, efficiency in percent are usually indicated.

Using this data, engine power in hp is calculated. according to the formula:

(V x I x Efficiency): 746 = HP

Efficiency is converted to decimal fraction - in the form of decimal fraction 82%.

The second way to determine power in hp
The voltage, current, efficiency are multiplied, then divide the result by 746. So, if the voltage is 240 V, the current is 5 A, the efficiency is 82%, then the power is in hp. will be 1.32 hp

Conclusions and useful video on the topic

Horsepower Details:

Increasingly, power is indicated in kilowatts, and non-system units are a thing of the past. Yet the need for horsepower conversion still exists. As long as these units exist, you must be able to use them wisely.

Have questions about the topic of the article? Or maybe there is information that could complement our material? Please write your comments, share your experience in the block below.

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Visitors Comments
  1. The above formulas, in fact, determine not the power of the car, but the effective power of its engine. Agree that not all power goes to the wheels. Handouts, transmission and other little things like power steering or climate control take "their share". Plus, we do not take into account all kinds of resistance forces, so the real error in determining power will be in the region of 5-10%.

    I also add that there are other ways to determine power, for example, by engine displacement or acceleration time of a car up to 100 km / h. And tuning lovers use more exotic methods, say, based on the performance of the injectors.