Horsepower Vs Kilowatts: A Practical Guide for Machine Builders and Maintainers

As a professional in the assembly and/or maintenance of machines, you will doubtless be involved in any of a broad range of specialised tasks. These duties could include specifying motors, sizing systems, and/or simply ensuring certain machinery keeps on operating effectively.

Your work will also necessitate you grasping certain concepts, units of measurements, and the distinctions between them – not least as far as horsepower and kilowatts are concerned.

So, in this article, we will outline some practical information and advice that will help you better understand the differences between these units, and why they matter.

First, What Are Horsepower and Kilowatts?

While both these units measure power, they are rooted in profoundly different histories and worlds. Sure enough, they tend to be used in different regions and contexts.

In summary:

• Horsepower (hp)

This is a measurement of power or the rate at which work is done. It denotes an internal combustion engine or electric motor’s relative strength, with one mechanical (imperial) horsepower being the amount of energy required to lift a 250kg weight by one foot every second.

The term "horsepower" is a throwback to the days when horses were the primary means of transportation, although it was actually coined in the steam age, during the late 18th century. Its emergence was essentially due to Scottish inventor James Watt’s wish to compare the power output of his steam engines to that of horses.

• Kilowatts (kW)

This is a unit of power whereby one kilowatt equals 1,000 watts. Like horsepower, it can be used for both internal combustion and electric machinery. However, it does tend to be particularly strongly associated with the latter. This should be unsurprising, given that it is a purer signifier of electric power.

You might have seen kW used instead of hp in the car reviews and manufacturer literature in certain countries, such as Australia – even in the case of vehicles with internal combustion engines. In European countries, meanwhile, kW became the officially recognised measurement of engine power in 1972.

But Isn’t There a Distinction Between Imperial Horsepower and Metric Horsepower?

Yes, there is, although the difference is relatively subtle:

• One imperial (also known as "mechanical") horsepower to equal to 745.7 watts, or 0.75 kilowatts
• One metric horsepower is equal to around 735.5 watts, or 0.74 kilowatts

For machine builders and maintainers, of course, even the most "subtle" differences matter. So, you will need to be careful in ensuring you don’t mix up imperial and metric horsepower measurements.

As the van leasing experts at Vanarama explain, this slight gap means a car with 100 metric horsepower would actually have 98.94 imperial horsepower.

To add further potential for confusion, even in a context in which the right type of horsepower measurement is used, this might be seen rounded up in certain contexts. So, that 98.94 – for example – may be referenced as 99.

The term "brake horsepower" is frequently used in the UK; this is another term used to refer to mechanical or imperial horsepower, rather than metric horsepower.

Why Is It So Crucial for Machine Builders and Maintainers to Know All This?

These units of power measurement have a variety of applications in machine building and the associated maintenance. Kilowatts, for instance, tend to be the preferred unit for industrial machinery, while for internal combustion engines in the heavy equipment industries, horsepower may be used.

So, it is vital for workers in these fields to be well-versed in these units, and to know how to switch between them. You might undertake such calculations manually using the relevant multipliers. Alternatively, you may favour using a widely trusted calculator – such as the one available on the RS Online website – to convert horsepower to kilowatts accurately online.

The more you know as a professional in these fields about these units of power measurement and how they differ, the more strongly placed you will be to build and maintain high-quality, potent, and long-lasting machinery.

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