A Quick Note on Horsepower

My Grandpa Phil and his team of horses in Central Wisconsin

If you want to appreciate the impact of energy and power in your everyday life, I can’t recommend the book Energy and Civilization by Vaclav Smil highly enough.

For me, the book also helped me understand more about my family history and provided a window into their daily lives, especially his discussion on horsepower.

I come from a long line of farmers in Central Wisconsin. Both of my grandpas eventually bought tractors for the farm work, but when they were kids, almost all of the work that wasn’t done by humans was done using horses. True to his name, my Grandpa Phil loved horses and used them on the farm as an adult.

Horsepower (hp) is a unit of power, measuring the rate at which work is done, and it quantifies the output of mechanical devices, especially engines. The term gained steam—no pun intended—in the late 18th century when James Watt developed important improvements to the steam engine and needed a way to market his invention in a unit that his potential customers could easily understand: horsepower.

Watt’s horsepower measured the amount of work one horse could steadily perform throughout the course of an entire day on a sustained basis, not the maximum power a horse could provide in short bursts, which can be as high as 15 horsepower.

A human can work at a steady rate of about 0.13 horsepower, meaning a horse can perform about 7.5 times more work than a human over the course of a day. This means my Grandpa Phil was able to do about 15 times more work over the course of the day, thanks to his team.

It’s one thing to read about horsepower and its impact on productivity, but if you want to feel the difference between horsepower and no horsepower, try using a rotary blade push mower to mow a quarter-acre yard —like I foolishly did when we first bought our house— and then do the same thing with the gas-powered lawnmower.

Once was enough for the rotary mower, but it was not lost on me that the small, gas lawnmower I purchased has a four-horsepower engine, which means the small machine in my garage does twice as much work as my grandpa’s horses could or the equivalent sustained output of 30 men.

The lawnmower also helps explain the economics of why the horses eventually lost their jobs to cars, trucks, and tractors.

The thing about horses is that it takes a lot of energy—also known as food—to keep them alive, whether they are performing useful work or not. A fully-grown horse needs about half a small square bale of hay per day, which can cost anywhere between $3 and $6 per bale. Meaning keeping two horses fed for a month would cost about $180, not including grain or other feed.

In contrast, the lawnmower is not a gas guzzler. I can mow the lawn three or four times on a gallon of gas, which means my fuel bill is about a dollar per mow, and I only need to “feed” it when it is doing useful work for me, and taking care of it requires far less work than horses.

My Grandpa Orr was full of stories— most of them about growing up in the Great Depression or dealing feeder pigs— but one story about horses sticks with me.

He was born the youngest of six kids in 1930, and his dad died when he was three years old. The family was always short on money, so they couldn’t afford a tractor, and so they had to use horses.

He said they always had two horses; one was generally okay, and the other was an old nag that would die every winter. Every year, the one that was okay the year before would turn into the nag that would die in the winter.

Cars, trucks, tractors, and lawnmowers can have equipment malfunctions, but they don’t founder and they don’t die. New parts can be obtained—albeit not always cost-effectively— and they can often be made to continue running for a long time, performing the necessary work we need to improve our lives.

According to the Wisconsin Farmer, by 1920, America had more than 25 million horses and mules, most of which were used for farm work, as reported by the National Agricultural Statistics Service. But this was “peak workhorse.”

In 1920, tractors constituted just 10.8 percent of on-farm horsepower; by 1930, this had increased to 40 percent. By 1940, it had risen to 64.8 percent, and by 1950, to 87.7 percent. By 1960, it had reached 96.6 percent. In 40 years, the horse went from providing 89.2 percent of the useful non-human work done on farms to 3.4 percent.

Thanks for reading this rambling edition of Energy Bad Boys. Check out the podcast Mitch and I did with

Gabriella Hoffman

about the true cost of rising electricity prices.

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