Why is engine power measured in horsepower: from steam engines to modern cars

From steam engines to supercars: how horsepower became a measure of power

Have you ever wondered why your car's engine power is measured in horsepower - a unit that seemingly has nothing to do with iron and gasoline? After all, not a single modern engine works on the basis of horse traction, and horses themselves have long given way to technology. It turns out that there is a fascinating history behind this unit of measurement, connected to the industrial revolution, marketing moves and even... beer barrels!

Today horsepower (hp) is not just a tribute to tradition, but an officially recognized unit of power that is used all over the world. But why didn’t engineers switch to more accurate and modern units like watt or kilowatt? The answer lies in the psychology of perception, the convenience of comparison, and even in the legal norms of some countries. In this article we will figure out how one horse became the standard for measuring the power of cars for centuries, and why this unit is still relevant despite the development of technology.

Who invented horsepower: the story of James Watt and beer barrels

It all started in 1782when the Scottish engineer James Watt - the inventor of the steam engine - was faced with a problem: how to explain to customers how much more powerful his machine is than its competitors? In those days, the main “driving force” of industry was horses, which pulled loads, turned millstones, and even pumped water from mines. Watt decided to use this image for marketing.

Legend has it that the engineer observed the horses at work in the brewery, where they pulled the yoke that lifted the barrels of beer. He calculated that one horse could lift a load weighing 33,000 lb (≈15 tons) to the height 1 ft (30 cm) for 1 minute. This is how the first one appeared horsepower — horsepower (hp). Watt later refined his calculations and determined that 1 hp = 745.7 W (watt is a unit named after him!).

• 🐎 The Myth of Accuracy: In fact, a real horse is capable of developing power up to 10–15 hp in a short-term mode, but Watt took as a basis average workload.
• 🍺 Beer connection: The first "tests" were carried out at the brewery Whitbread in London - the horses there were well trained and hardy.
• ⚙️ Marketing move: Watt exaggerated the power of his machines by 50% to lure customers away from competitors. This is how it appeared metric horsepower (1 HP = 735.5 W).

Horsepower vs. watts: why automakers don't switch to kilowatts

From a physics point of view, horsepower is an obsolete unit. B 1960 on XI General Conference on Weights and Measures was accepted International System of Units (SI), where power is measured in watts (W). So why do automakers still use hp?

It's all about buyer psychology. Number 200 hp sounds more impressive than 147 kW (and this is the same thing!). Moreover, in some countries, such as USA and Japan, horsepower stipulated in the laws on transport taxes. And in Germany until 2021, the cost of insurance directly depended on the quantity hp under the hood.

Country	Official unit of power	Is HP used? in the documents?	Example (150 hp)
Russia	kW (SI)	Yes (PTS, taxes)	110.3 kW
USA	hp (horsepower)	Yes (all documents)	150 hp
Germany	kW (kilowatts)	Yes (insurance, taxes)	110.3 kW (but also indicate 150 PS)
Japan	PS (Pferdestärke)	Yes (tax system)	150 PS

⚠️ Attention: In Russia since 2010 PTS power is indicated in kilowatts, but are still used in advertising and colloquial speech hp. This can lead to confusion: for example, 100 kW ≈ 136 hp, not 100!

How much horsepower is in an electric car: why Tesla is ahead of gasoline cars

Electric motors have a fundamentally different power character. If in a gasoline engine peak power is achieved only at certain speeds, the electric motor produces maximum torque from zero. Therefore compare hp electric cars and internal combustion engines directly is incorrect.

For example, Tesla Model S Plaid has 1020 hp, but its engines develop 10,000 Nm torque is in 5–10 times morethan that of supercars with internal combustion engines. At the same time, the electric motor weighs several times less and does not require a gearbox. This is why electric cars accelerate so quickly: 0–100 km/h in 2 seconds at the same Model S - a result unattainable for most gasoline cars.

Why don't electric cars need a gearbox?

The electric motor is effective over the entire speed range (from 0 to 20,000 rpm), while the internal combustion engine has a maximum power “shelf” only in a narrow range (usually 4000–6000 rpm). Therefore, electric cars do without multi-stage gearboxes, using a single-stage gearbox.

• ⚡ Instant response: The electric motor reaches peak power in 0.1 seconds, while internal combustion engines are for 0.5–1 second.
• ⚖️ Weight vs. power: Electric motor Tesla weighs ~50 kg and produces 500+ hp, while a gasoline V8 of similar power produces 200+ kg.
• 🔋 Efficiency: The electric motor is efficient 90–95%, while internal combustion engines are only 20–30% (the rest is lost in heat).

How horsepower is measured today: dynamometers and standards

Modern automakers use dynamometers for accurate power measurement. The motor is connected to dynamometer, which creates a load and measures torque and speed. Then the formula calculates the power in hp or kW.

But there is a nuance here: there are different measurement standardswhich give different results for the same engine! For example:

• 🇪🇺 DIN (Germany): Power is measured without attachments (generator, pump, etc.). The result is below at 10–15%.
• 🇯🇵 JIS (Japan): Measured with attachment but without exhaust system. The result is higher by 5–10%.
• 🇺🇸 SAE (USA): Two options: SAE net (with hinged) and SAE gross (without attachment, as in the 60s). The difference can reach 20%!

⚠️ Attention: If the technical specifications indicate 200 hp (DIN) and 220 hp (SAE gross), we are talking about the same engine! This is not “overclocking” by the manufacturer, but different measurement methods.

Horsepower and taxes: how power affects the cost of owning a car

In many countries, engine power directly affects transport tax, insurance and even registration fees. For example, in Russia the tax rate depends on the quantity hp:

Power (hp)	Tax rate (RUB/year, 2026)	Example car
up to 100	2,5–7	Lada Granta, Kia Rio
101–150	20–35	Toyota Camry, Volkswagen Passat
151–200	45–75	BMW 3 Series, Audi A4
201–250	110–150	Mercedes-Benz E-Class, Lexus GS
over 250	300–500+	Porsche 911, Ferrari 488

Interestingly, in some regions of Russia (for example, in Moscow and St. Petersburg) rates are higher than the national average. And in Germany until 2021, insurance was calculated according to the formula, where hp were multiplied by the risk coefficient of the model.

The future of horsepower: why they won't be replaced by kilowatts

Despite the fact that watt - official SI unit, horsepower remain in use for several reasons:

1. Tradition: For 200+ years the term has become part of car culture. The phrase "200 horses under the hood"causes emotions as well"147 kilowatts" - no.
2. Legal rules: B USA, Japan and some European countries hp enshrined in laws on certification and taxes.
3. Ease of comparison: For most drivers, it is easier to estimate power in hpthan to translate kW in my head.
4. Marketing: Manufacturers know that 500 hp sounds more impressive than 368 kW, and use it in advertising.

At the same time, in Europe there is a gradual transition to kilowatts - for example, in the technical data sheets of new cars, power is indicated in both units. But complete refusal hp unlikely: it is too ingrained in the minds of car enthusiasts.

FAQ: Frequently asked questions about horsepower

❓ How many kilowatts are in one horsepower?

It depends on the standard:

• Metric HP (PS): 1 hp = 0.7355 kW (used in Europe and Russia).
• Mechanical HP (hp): 1 hp = 0.7457 kW (USA, UK).

To translate kW in hp, multiply by 1,36 (for metric system).

❓ Why is power indicated in kilowatts in PTS, but in horsepower in advertising?

In Russia from 2010 in official documents (PTS, STS), power is indicated only in kW - this is a requirement of the technical regulations of the Customs Union. However, in advertising and colloquial speech they still use hp, since this is more familiar to buyers.

For example, if the PTS says 110 kW, then in hp it will be 150 hp (110 × 1,36 ≈ 150).

❓ Is it possible to increase the horsepower of your car?

Yes, there are several ways:

• Chip tuning: Flashing the ECU to optimize the fuel mixture and ignition (+10–30 hp).
• Turbine/compressor installation: Forced boost can add 50–100+ hp, but requires engine modification.
• Exhaust system replacement: Direct-flow exhaust improves gas removal (+5–15 hp).
• Increase in working volume: Boring the cylinder block or replacing pistons (requires a complete engine overhaul).

⚠️ Important: Any power changes must be made to the title, otherwise there will be problems with passing inspection and insurance.

❓ Why do electric cars have more power, but less consumption?

Electric motors convert 90–95% battery energy into motion, while the internal combustion engine loses 70–80% fuel energy into heat, friction and exhaust. Therefore, to accelerate, an electric car needs fewer “horses” than a gasoline car with similar dynamics.

For example, Tesla Model 3 Performance has 450 hp, but spends the equivalent 15–20 l/100 km in terms of gasoline. For comparison, BMW M3 with 430 hp spends 10–12 l/100 km - in 2 times more!

❓ What is the most powerful car in the world in terms of horsepower?

On 2026 the record belongs to a hypercar Devel Sixteen — 5007 hp (according to the manufacturer). However, the highest power production models are:

• Bugatti Chiron Super Sport 300+ — 1600 hp
• Rimac Nevera (electric car) — 1914 hp
• Koenigsegg Jesko Absolut — 1600 hp (on bioethanol - up to 1800 hp)

For comparison: the first Ford T (1908) had only 20 hp!