Understanding engine power units is essential when comparing vehicle performance across different regions and standards. We express engine power in kilowatts (kW) or horsepower (HP). However, not all horsepower is the same, and understanding engine power units can be quite complicated.

How It All Started
The Origins of Engine Power Measurements

Understanding engine power units begins with the historical context: Scottish engineer James Watt developed the concept of horsepower in the late 18th century to compare the power of steam engines to that of horses. He defined one horsepower as the power needed to lift 550 pounds (about 250 kg) by 1 foot (about 30 cm) in one second. This gave rise to the imperial horsepower, abbreviated as “hp.”

Then Comes the Twist…

When understanding engine power units, it’s important to note that countries using the metric system found it impractical to define power using pounds and feet. So, we adapted a similar formula for the metric system. Instead of using one foot or 30 cm, we used a height of exactly 1 meter and adjusted the mass accordingly. This gave the definition: one metric horsepower is the power needed to lift 75 kg to a height of 1 meter in one second.

This is why 1 metric horsepower equals 0.9863 imperial horsepower.

Countries use different abbreviations for metric horsepower, depending on the language:

• PS – from Pferdestärke in German
• CH – from chevaux-vapeur in French (not the same as CV in France!)
• CV – from cavallo vapore in Italian
• PK – from paardenkracht in Dutch
• HK – from hestekraft in Norwegian

Other examples include:

• Spain: caballo de vapor – CV
• Portugal: cavalo-vapor – CV
• Russia: лошадиная сила – л. с.
• Sweden: hästkraft – hk
• Finland: hevosvoima – hv
• Czech Republic: koňská síla – k or ks
• Slovakia: konská sila – k or ks
• Romania: cal-putere – CP

These abbreviations can appear in both upper or lower case, regardless of what is “officially” correct.

And an Even Bigger Twist

As you continue understanding engine power units, you’ll come across BHP, or “brake horsepower,” a unit mainly used in the UK (and formerly in the US). The problem arises because experts have debated the definition of “brake horsepower” and how to measure it.

It’s hard to explain this without understanding how engine power measurement methods and procedures have changed over the past hundred years in various countries.

A widely accepted definition is that BHP measures power with the consumers (like lights, electronics, alternator, etc.) on, whereas “HP power” measures power without these consumers on. So, an engine’s power is always higher when expressed in HP compared to BHP.

However, not everyone agrees with this definition. Some experts argue that it may have been true 40-50 years ago, but things have changed significantly since then. After further investigation, we realized it’s not worth the time and energy—let’s leave it to the engineers who know the history well to establish the facts.

For more details on how different power metrics impact vehicle performance, see our article on Understanding Car Performance Metrics.

Nothing Without the Dyno!

Next in understanding engine power units is WHP, or “wheel horsepower.” This is simple—”wheel” refers to the wheel in English, so WHP measures power at the wheels (on a dynamometer or so-called “dyno rollers”).

Someone might think that WHP should be the universal unit of power because it measures the “real” power transmitted to the wheels/ground. Unfortunately, the same dynamometer can show different measurements when testing the same car, depending on various factors. So, the results from these devices are not reliable enough to establish an official power unit.

So, What’s the Solution?

The solution is already in place—kilowatts (kW) or horsepower (HP, PS, CV, etc.). We just need to know the source of what we are reading.

Converting Engine Power Units: Essential Equivalencies

To accurately understand engine power, conversions between units are essential. For example:

So, 1 KS = 1 PS = 1 CV = 0.736 kW.

In other words, 1 kW = 1.36 KS = 1.36 PS = 1.36 CV.

Moreover, 1 kW = 1.341 HP.

Finally, 1 HP = 0.99 BHP.

Various calculators can help. First and foremost, Google can calculate what you need—just type, for example, “136 PS to kW” if you want to see how many kilowatts a 136 “horsepower” car has.

Understanding engine power units is crucial for making informed decisions when comparing vehicles. By grasping the differences and similarities between these units, you can better interpret vehicle specifications and performance.