Where did the concept of “horsepower” come from and why is it still used in the auto industry?

Term "horsepower" has firmly entered the vocabulary of every car owner, but few know that behind it is not just an abstract unit of measurement, but a whole history of technical progress. Today we are accustomed to seeing this value in the characteristics of engines - from modest low-power engines to supercars with hundreds hp under the hood. But how and why did the horse become the standard for measuring power? And why, despite the transition to the metric system, horsepower are they still used on car documents?

In fact, the appearance of this term is associated with the industrial revolution and the need to compare the efficiency of steam engines with the draft power familiar to humans. But why the choice fell on the horse is not only a technical, but also a cultural question. In this article we will look at who came up with the idea horsepower, how it was calculated in the 18th century, and why today it causes controversy among engineers and car enthusiasts.

Spoiler: modern horsepower have long been unequal to the real strength of one horse - and this is not the only paradox that this unit of measurement hides.

Who coined the term "horsepower"?

The authorship of the concept belongs to the Scottish engineer and inventor James Watt - the very one whose name now bears the unit of power in the SI system (watt). At the end of the 18th century, Watt worked on improving steam engines, which were then actively introduced into production. The main problem was to explain to potential buyers how his car outperforms horses - the main “engine” of that time.

Legend has it that Watt observed horses working in coal mines, where they used pulleys to lift loads. He noticed that on average one strong horse could lift a load weighing 33,000 pounds (about 15 tons) to height 1 foot (30 cm) per 1 minute. It was this empirical indicator that formed the basis of the calculations.

However, technical historians claim that Watt exaggerated the horse's actual capabilities by about 50%, most likely for marketing purposes. The fact is that the average workhorse is capable of developing power of about 0.7–0.8 hp by modern standards, and not a whole unit. However, the standard took root, and by the beginning of the 19th century horsepower has become a generally accepted quantity in engineering calculations.

• 🔧 James Watt - not only the “father” of horsepower, but also the inventor of the centrifugal regulator, which is still used in some mechanisms.
• 📜 The first official mention of the term dates back to 1782 - it was then that Watt introduced it into circulation to describe the power of his steam engines.
• 💰 Interesting fact: Watt received a royalty of 1/3 of the coal savings that his cars provided compared to horses.

How was horsepower calculated in the 18th century?

Watt's original calculation was based on observations of horses spinning millstones. He determined that one horse could produce power equivalent to lifting 550 pounds (≈250 kg) to height 1 foot for 1 second. This value became the standard for mechanical horsepower (horsepower, hp).

However, different countries have their own calculation options:

• 🇬🇧 British horsepower (hp) — 745.7 W (used in the US and UK).
• 🇫🇷 Metric horsepower (PS) — 735.5 W (adopted in most European countries, including Russia).
• 🇯🇵 Japanese horsepower - equal to metric, but sometimes rounded to 735 W.

The difference arose due to the fact that in continental Europe they took kilograms and meters as a basis, rather than pounds and feet. For example, metric hp defined as the power required to lift 75 kg to the height 1 meter for 1 second.

Why did the USSR use the metric system?

The Soviet Union, like most European countries, adopted metric horsepower (PS) because it fit better with the decimal system. At the same time, the documents often indicated the power in watts for accuracy.

⚠️ Attention: In technical data sheets of cars sold in Russia, power is indicated in kilowatts (kW) with a mandatory note in brackets about transfer to hp according to the metric system. For example: 100 kW (136 hp).

Why is horsepower still used in the auto industry?

Despite the fact that power is officially measured in the SI system in watts, horsepower remain popular for several reasons:

1. Historical inertia. The term has taken root more 200 years ago, and automakers continue to use it for marketing purposes - figures in hp are perceived as more “tangible”.
2. Psychological factor. For most people 200 hp sounds more impressive than 147 kW, although it's the same thing.
3. Legislative norms. In some countries (for example, Japan) the tax on cars depends on the power in hp, not in kW.

In addition, in motorsport and tuning, power is traditionally indicated in hp, as it is an established standard for comparing engine performance. For example, in the formula "100 hp per ton of weight» It’s easier to evaluate the dynamics of the car.

Country/Region	Designation	Watt equivalent	Application
UK, USA	hp (horsepower)	745.7 W	Cars, equipment
Europe, Russia	PS (Pferdestärke)	735.5 W	Official documents
Japan	PS	735.5 W	Taxation
France (until 1972)	ch (cheval-vapeur)	735.5 W	Historical documents

How many real horses are there in one “horsepower”?

This is where the fun begins. According to Watt's initial calculations, one horsepower must correspond to the work of one horse. But in practice, everything is not so clear:

🔬 Scientific experiments show that the average horse can develop power up to 14–15 hp in short bursts (for example, when starting from a place). However, during long-term work (for example, plowing or transporting goods), its power drops to 0.5–1 hp due to fatigue.

🐎 Record holders among horses (for example, heavy trucks) at peak loads can produce up to 20 hp, but again - only for a short time. For comparison: a person during intense physical activity develops a power of about 0.1–0.2 hp.

• 🏇 Thoroughbred racehorse at a gallop: up 12–15 hp
• 🐴 Work horse (draft horse): 1–2 hp in long-term work
• 👨 Man cyclist (professional): up to 0.5 hp at short distance

⚠️ Attention: If the technical specifications of the vehicle indicate 150 hp, this does not mean that the equivalent of 150 horses is working under the hood. Actual motor watts are always more accurate - check both values!

How to convert horsepower to watts and back?

For translation hp in watts and vice versa, fixed coefficients are used, but here are the basic formulas:

Metric Horsepower (PS):

1 hp = 735.49875 W ≈ 0.7355 kW
1 kW ≈ 1.3596 hp

British/American horsepower (hp):

1 hp = 745.699872 W ≈ 0.7457 kW
1 kW ≈ 1.3410 hp

In practice the difference between hp and PS is about 1,4%, which is not critical for everyday calculations, but can be important in engineering problems.

Check which hp Power indicated (metric or imperial)|

Use the exact ratio (735.5 for PS, 745.7 for hp)|

Check the result on a calculator (for example, RapidTables)|

Please note that car documents usually use the metric system (PS)

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Example: if the PTS indicates 120 hp, then in kilowatts it will be:

120 × 0.7355 ≈ 88.26 kW

Horsepower in the modern world: myths and reality

Today horsepower became more of a tribute to tradition than a technical necessity. However, there are still many myths surrounding it:

🚗 Myth 1: “The more horsepower, the faster the car.”

Reality: Power is only one of the dynamics factors. Also important torque, vehicle weight, gearbox ratios and aerodynamics. For example, a diesel engine with 150 hp can be faster than gasoline 180 hp at low speeds.

💰 Myth 2: “In Russia, power tax is calculated by horsepower.”

Reality: C 2020 transport tax in the Russian Federation is calculated based on kilowatt, but in most regions they still use the conversion factor 1 hp = 0.7355 kW for convenience.

⚡ Myth 3: "Electric cars don't have horsepower."

Reality: The power of electric motors is also measured in hp or kW. For example, Tesla Model S Plaid develops 1020 hp (760 kW), which is comparable to supercars.

• 🔋 Electric cars often have instant torque, which makes them accelerate faster than gasoline counterparts with the same power in hp
• 🛢️ Turbocharged engines may temporarily exceed the declared power due to supercharging (the so-called “overboost”).
• 🏁 Racing cars Power on "special fuel" is often quoted as being 10–20% higher than the production version.

The future of horsepower: will it remain relevant?

With the transition to electric vehicles and stricter environmental regulations, the question of the future horsepower is becoming more and more relevant. Here are some trends:

🔌 Electrification. Manufacturers of electric cars (for example, Tesla or Rimac) more often indicate power in kilowatts, since this more accurately reflects the characteristics of electric motors. However, for marketing they often duplicate the meaning in hp.

🌍 Environmental standards. In the EU with 2026 emission requirements are planned to be tightened, and engine power may become a secondary parameter compared to specific fuel consumption or efficiency.

📊 New units of measurement. Some experts suggest switching to power density (hp per ton of weight) or power per liter of engine volumeto compare cars more objectively.

However, complete refusal horsepower unlikely - their cultural and historical value is too great. Most likely, they will remain in documents and marketing, but more precise metrics will be indicated nearby kW or Nm (newton meters for torque).

FAQ: Frequently asked questions about horsepower

❓ Why are there different horsepowers in the USA and Europe?

In the USA they use British horsepower (hp), equal to 745.7 W, and in Europe - metric (PS), equal to 735.5 W. The difference arose due to different systems of measurement (feet/pounds vs meters/kilograms). For example, 100 hp in America this is approximately 101,4 PS in Europe.

❓ How much horsepower does a person have?

The average person under short-term exertion (for example, sprinting) can develop power up to 0.1–0.2 hp (75–150 W). Professional cyclists reach peak fitness 0.5 hp (370 W), but not longer than a few minutes.

❓ Why is the power indicated in kW and hp in the PTS?

According to international standards (in particular the EU directive 80/181/EEC), power must be indicated in kilowatts as the basic SI unit. However, for the convenience of car owners, the value is duplicated in hp according to the metric system (PS).

❓ Is it possible to increase engine horsepower without tuning?

Yes, there are several ways:

• 🔧Usage high octane fuel (for example, AI-98 instead of AI-92).
• 🔥 Chip tuning (reflashing the ECU) to optimize fuel supply and ignition.
• 🚿 Installation sports air filter (for example, K&N).
• 🛢️ Application additives for cleaning the fuel system (for example, Liqui Moly).

However, the increase usually does not exceed 5–10%, and incorrect actions can reduce engine life.

❓ Why do they still use horsepower in motorsport?

Tradition and ease of comparison. For example, in Formula 1 or NASCAR Engine power is indicated in hp, since it is more familiar to spectators and teams. In addition, the numbers are in the hundreds hp look more spectacular than the kilowatt equivalent.