Horsepower in a car: what is it actually measured in and why is it important for the driver

Have you ever wondered why engine power is measured in horsepower, and not in the more familiar watts or kilowatts? This term came to us from the 18th century, when a Scottish engineer James Watt was looking for a way to explain to customers how much more productive his steam engines were than live horses. Today hp is not only a historical artifact, but also a key parameter on which car taxes, cost OSAGO insurance, as well as the real dynamic characteristics of the machine.

In Russia and many other countries horsepower are still used in parallel with kilowatts (kW) - the official unit of measurement of power in the SI system. But here lies the catch: 1 hp ≠ 1 kW, and their ratio depends on the standard by which they are calculated. Moreover, different countries have their own “horses”: German, American, British and even Japanese. Let's figure out how not to get confused in these units and why power in PTS may not coincide with the real one.

Spoiler: if you plan to buy a car second-hand or import it from abroad, know the nuances of measurement hp will help you save on taxes and avoid problems with the traffic police. And this information will protect owners of powerful cars (from 250 hp and above) from fines for incorrectly specified data in documents.

1. What is horsepower: definition and history of the term

Horsepower (hp) is a non-systemic unit of power that historically equaled the work done by one horse per unit of time. James Watt introduced this concept to 1782to demonstrate the advantages of their steam engines over animals. According to legend, an engineer watched a horse lift coal from a mine using a block, and calculated that in a minute it could lift 33,000 pounds (≈15 tons) to height 1 foot (≈30 cm). This is how it appeared mechanical horsepower.

However, modern research shows that a real horse is capable of developing power up to 14.9 hp (according to standard SAE), but only in short bursts. Long-term work at the level 1 hp for an animal it is already considered hard work. It's interesting that in Germany and Scandinavia the term is still used Pferdestärke (PS), which literally translates to “horse strength”, and in English-speaking countries - horsepower (hp).

Today horsepower - This is more a tribute to tradition than a practical unit. Officially used in physics and engineering watts (W), but in the auto industry hp remain popular due to:

• 📜 Historical habit (drivers and mechanics are accustomed to operating with these numbers).
• 💰 Tax and insurance calculations (in Russia, the transport tax rate is tied to hp).
• 🏁 Marketing purposes (manufacturers often indicate power in hp as a more “spectacular” value).

But here comes the problem: different countries use different hp standards., and this can be confusing. For example, American HP (hp) not equal European (PS), and British (bhp) generally has its own unique meaning. More about this in the next section.

2. Types of horsepower: what is the difference between hp, PS, bhp and others

If you think that 1 hp = 1 hp, then you are very mistaken. In the world there is at least 5 different standards horsepower measurements and values may vary by 1–5%. This is important to consider when buying an imported car or comparing the characteristics of models from different countries.

Let's look at the main types:

• 🇪🇺 Metric HP (PS, cv, ch) — used in Europe and Russia. 1 PS = 735.49875 W (rounded 0.7355 kW). This standard has been adopted in most countries, including Germany, France and Italy.
• 🇺🇸 Mechanical HP (hp, SAE) - American standard. 1 hp = 745.69987 W (≈0.7457 kW). Often found in documentation for cars from the USA.
• 🇬🇧 British HP (bhp, IHP) - used in the UK. 1 bhp = 745.7 W (almost identical to the American one, but calculated using a different method).
• 🇯🇵 Japanese HP (JIS) - standard adopted in Japan. 1 JIS hp ≈ 735.5 W (close to metric, but with nuances in measurement).
• 🔧 Boiler HP (boiler hp) - an outdated standard for steam engines. 1 boiler hp ≈ 9809.5 W (used extremely rarely).

In practice this means that American car with 300 hp actually has ~296 PS (metric hp). The difference seems insignificant, but when calculating vehicle tax or insurance, it can play a role. For example, in Russia the tax rate for cars is over 250 hp significantly higher, and the error is 4–5 hp. may result in overpayment.

In addition, there are electric hp (746 W) and hydraulic hp (745.7 W), but they are practically not used in the automotive industry.

Why did the USSR use the metric hp system?

In the Soviet Union, as in most socialist countries, they adhered to the metric measurement system, so engine power was indicated in hp (PS) according to DIN standard (Deutsche Industrie Norm). This was convenient for unifying documentation and calculations, especially when exporting cars to Eastern European countries. It is interesting that on some Soviet engines (for example, ZIL-130) power was indicated in both hp and kW - to comply with international standards.

3. How to convert horsepower to kilowatts and back: formulas and examples

Since kilowatt (kW) is the official SI unit of power, and horsepower — non-systemic, it is often necessary to convert some values into others. This is relevant for:

• 📄 Registration of documents (in PTS, power can be indicated in kW, and the tax is calculated by hp).
• 🔧 Engine diagnostics (some stands provide results in kW).
• 🛒 Car comparisons (manufacturers from different countries may use different units).

Basic translation formulas:

• 🔹 From HP (metric, PS) to kW: kW = hp × 0.73549875
• 🔹 From kW to hp (PS): hp = kW × 1.35962162
• 🔹 From US hp to kW: kW = hp × 0.74569987

Examples of calculations:

• 🚗 Car with power 150 hp (PS) in kW: 150 × 0.7355 ≈ 110.3 kW.
• 🚛 Truck with power 400 hp (SAE) in kW: 400 × 0.7457 ≈ 298.3 kW.
• ⚡ Electric motor with power 100 kW in hp: 100 × 1.36 ≈ 136 hp.

Important: in Russia, metric horsepower (PS) is used to calculate transport tax, even if the documents indicate power in kW. Therefore, when buying an imported car, always check what standard the power is specified by!

Power in hp (PS)	Power in kW	Power in hp (SAE)	Example car
100	73,55	98,63	Lada Vesta 1.6
200	147,10	197,26	Volkswagen Golf GTI
300	220,65	295,89	BMW M3 (F80)
500	367,75	493,15	Mercedes-AMG E63 S

4. Why the power in the PTS may not coincide with the real one: let’s understand the reasons

Many car owners are faced with a situation where power in PTS does not coincide with the data from the manufacturer’s catalog or the results of measurements on a dynamometer. The difference can reach 10–15%, and here's why:

🔧 1. Different measurement standards

• 📏 DIN (Deutsche Industrie Norm) — power is measured without attachments (generator, air conditioner, etc.). This is a “clean” indicator of the motor.
• 📏 SAE (Society of Automotive Engineers) - American standard, where power is measured from a piece of attached equipment. Results are usually higher by 5–10%.
• 📏 ECE (Economic Commission for Europe) - European standard, close to DIN, but with some amendments.

📊 2. Rounding in documents

In PTS, power is indicated in whole numbers, while real power can be, for example, 147.8 hp. In the docs this will be rounded up to 148 hp, but can show at the stand 145 hp due to measurement error.

🛠️ 3. Engine wear

Over time, motor power decreases due to:

• 🔥 Wear of the piston group (compression drops by 10–20%).
• 🛢️ Contamination of the fuel system (injectors, filters).
• 🌀 Deterioration of the turbine (if there is one).

📝 4. Errors in documents

Sometimes the power in the PTS is indicated by maximum value for this model, and not based on real measurements of a particular engine. This is more common in used foreign cars.

⚠️ Attention: If the power in the PTS is underestimated (for example, 190 hp is indicated instead of the real 210 hp), this can be considered violation when passing a technical inspection or registering for compulsory motor liability insurance. In some cases, the inspector may require a re-diagnosis.

Check the documents for errors (possibly a typo).

Compare the data with the manufacturer's catalog for your model and year.

Get it tested on a dyno (if the difference is significant).

Contact the traffic police to correct the data (if necessary).-->

5. How horsepower affects taxes, insurance and fines

In Russia horsepower directly affect three key expenses of the car owner:

1. 💰 Transport tax — the rate depends on engine power and region. For example, in Moscow in 2026 the following tariffs apply:
   • Up to 100 hp — 12 RUR/hp
   • 100–150 hp — 25 rub./hp
   • 150–200 hp — 35 RUR/hp
   • 200–250 hp — 50 rub./hp
   • Over 250 hp — 150 rub./hp

📋 Cost of OSAGO — insurance companies take power into account when calculating the tariff. The more hp, the higher the risk of an accident (according to statistics) and the more expensive the policy.

🚔 Fines for speeding - for cars with power over 150 hp There are increased fines for serious excesses (for example, 60+ km/h).

Example of transport tax calculation:

Car Toyota Camry 2.5 with power 181 hp in Moscow: 181 × 35 rub. = 6335 rub./year.

If the power were specified as 200 hp, the tax would increase to: 200 × 50 rub. = 10,000 rub./year.

Difference - 3665 rub. per year only because of inaccuracies in the documents!

⚠️ Attention: If you tuned the engine and increased power, but did not make changes to the PTS, this may lead to a fine of up to 5,000 rubles. (under Article 12.1 of the Code of Administrative Offenses of the Russian Federation for data inconsistency). In the event of an accident, the insurance company may refuse to pay if it turns out that the car has been modified.

6. Horsepower vs. torque: what is more important for car dynamics

Many drivers mistakenly believe that horsepower — this is the main indicator of speed and acceleration. Actually no less important torque (Nm), which determines how quickly a car can accelerate from a standstill and how it behaves at low revs.

Let's look at the differences:

• 🐎 Horsepower (hp) - show maximum powerwhich the engine can develop. Depends on them top speed car.
• 🌀 Torque (Nm) - shows rotation force crankshaft Depends on him acceleration and torque (e.g. ability to tow a trailer or climb a mountain).

Examples:

• 🚗 Honda Civic Type R - 320 hp, but only torque 400 Nm. This is a car for high revs and racing on the track.
• 🚛 Toyota Hilux - 204 hp, but torque 500 Nm. This engine is better suited for off-roading and towing.

In practice:

- For city driving more important torque at low speeds (so that you don’t have to “turn” the engine up to 4000 rpm to accelerate).

- For sport driving important horsepower at high speeds (to reach maximum speed).

- For SUVs and pickups priority - high torque (to overcome obstacles).

Formula for power and torque: Power (hp) = (Torque × Engine RPM) / 5252

This means that power depends on rpm: the same torque at 2000 rpm will produce less hp than at 5000 rpm.

Why are diesel engines more powerful than gasoline engines?

Diesel engines are developing maximum torque at low speeds (already from 1500–2000 rpm), while gasoline engines only from 3500–4500 rpm. For example, BMW 330d (diesel) has 265 hp. and 620 Nm, while gasoline BMW 340i at 340 hp gives out everything 450 Nm. Therefore, diesels are better suited for towing and off-road driving.

7. How to find out the real power of your car

If you doubt the data from the vehicle title or want to check whether the engine has lost power over time, there are several ways:

🔧 1. Dynamometric stand

The most accurate method. The car is driven onto a stand where the wheels rotate drums with sensors. The result is displayed in the form of a graph of power and torque by revolutions. Cost: 1500–3000 rub.

📊 2. Online calculators

You can use translation formulas or specialized services (for example, calc.ru). However, this will only give a theoretical value.

📄 3. Manufacturer's data

Find the technical specifications of your model on the official website or in the catalog. Please note that the standard power may be indicated there SAE (overestimated) or DIN (underestimated).

🔍 4. Diagnostic equipment

Some auto scanners (for example, Launch X431 or Bosch KTS) can read power from the engine ECU. However, this does not work on all machines.

📌 What to do if the power is lower than declared?

• 🔧 Check compression in cylinders (norm: 12–14 bar).
• 🛢️ Clear injectors and fuel system.
• 🌀 Check turbine (if any) for leaks and wear.
• 🔥 Replace spark plugs and high voltage wires.

⚠️ Attention: If after diagnostics it turns out that the power is underestimated by more than 15% of the nameplate, this may be a sign serious engine problems (piston wear, timing belt malfunction, etc.). In this case, a full diagnosis with analysis is recommended.

FAQ: Frequently asked questions about horsepower

❓ Why is power indicated in hp in the USA, and in PS in Europe? Are they the same thing?

No, these are different standards. 1 hp (SAE) ≈ 1,014 PS. The difference is small, but at large values ​​(for example, 500+ hp) it can reach 5–7 hp. This should be taken into account in documents for imported cars.

❓ What is the fine for non-compliance with power in the PTS?

If the power in the PTS is underestimated, this is considered design inconsistency (Article 12.1 of the Code of Administrative Offenses of the Russian Federation). Fine - 500–2000 rub., and in the event of an accident, the insurance company may refuse to pay. If the power is too high, you overpay the tax.

❓ Is it possible to increase engine power without changing the PTS?

Technically it is possible (chip tuning, replacing the turbine, etc.), but legally this is a violation. If changes are not made to the title, during inspection the traffic police may oblige you to return the engine to stock condition or fine you.

❓ Why do electric cars have high power but low torque?

This is a myth! Electric cars are developing maximum torque from 0 rpm (for example, Tesla Model S has 650 Nm at 1020 hp). However, the horsepower the peak is indicated, and the torque is constant, which creates the illusion of “weak” thrust.

❓Which engine is more powerful: gasoline or diesel with the same hp?

At the same power the diesel engine will have more torque due to higher torque at low speeds. Gasoline will perform better at high speeds (for example, when overtaking on the highway).