A bridge in Boston is measured in students. Physicists describe targets far smaller than an atom in barns. And somewhere, a radiation expert is counting bananas.
Metres, miles and minutes work fine for everyday life, but people have quietly invented a second, much stranger system. These are the weird units of measurement that actually exist. Some started as pranks, some are used by working scientists, and one is hiding in your car’s specs.
Weird units of measurement that started as a joke
The Smoot: The Bridge Measured in Students
In October 1958, MIT student Oliver Smoot lay down on the Harvard Bridge between Boston and Cambridge, Massachusetts. His fraternity brothers marked where his head was, he moved along, and he lay down again. And again, all the way across.
Smoot was 5 feet 7 inches (1.70 m) tall and was picked partly because he was the shortest pledge. The verdict: the bridge is 364.4 smoots long, “plus or minus one ear”.
Students still repaint the marks, and the halfway point at 182.2 smoots reads “Halfway to Hell”. When the bridge was rebuilt in the 1980s, police asked for the marks to stay because they used them to pin down accident locations.
The best twist? Smoot later chaired the American National Standards Institute and served as president of the International Organization for Standardization. The man who became a unit ended up in charge of standards. Google Earth even lets you measure in smoots.
The Sheppey: How Far Away Sheep Look Their Best
The sheppey is about seven-eighths of a mile (1.4 km). It’s defined as the closest distance at which sheep still look picturesque. Get any nearer and you start to notice the mud.
It comes from The Meaning of Liff, a spoof dictionary by Douglas Adams (author of The Hitchhiker’s Guide to the Galaxy) and John Lloyd that gives real place names new meanings. This one borrows the name of the Isle of Sheppey in England, and anyone who has walked past a field of sheep knows it’s accurate.
When scientists get silly
Some of the strangest units come from real laboratories, and scientists still use them.
The Barn: A Tiny Target With a Farmyard Name
In December 1942, American physicists Marshall Holloway and Charles Baker were having lunch at Purdue University. Working on the Manhattan Project, they needed a name for the unit that describes how likely tiny particles are to hit each other.
They considered naming it after colleagues, but “Oppenheimer” was too long and “Bethe” was too easy to confuse with the Greek letter beta. They settled on “barn”, because for a particle, a uranium nucleus is a target as big as a barn.
One barn is 10⁻²⁸ square metres: a decimal point, 27 zeros and a one. Particle physicists still use it, and the same joke produced even smaller units, the “outhouse” (a millionth of a barn) and the “shed” (10⁻²⁴ of a barn).
The Banana Equivalent Dose
Bananas are very slightly radioactive. They’re rich in potassium, and a small share of all natural potassium is radioactive potassium-40. A typical banana produces around 15 tiny radioactive decays every second.
So radiation experts turned it into a friendly unit. One banana equivalent dose is about 0.1 microsieverts, roughly what you get from eating one banana. On that scale, a chest CT scan is about 70,000 bananas.
Don’t give up your smoothie. Your body keeps its potassium level steady and gets rid of the extra, so bananas don’t build up radiation inside you. The unit is there for perspective, not panic.
The Beard-Second
The light-year measures huge distances by how far light travels in a year. The beard-second flips the idea: it’s how far an average beard grows in one second.
Google’s calculator puts it at 5 nanometres; one physics handbook says 10. It was meant for tiny distances, such as those inside computer chips. If you have a beard, it has grown about 20 beard-seconds while you read this paragraph.
The light-year measures huge distances by how far light travels in a year. The beard-second flips the idea: it’s how far an average beard grows in one second.
Google’s calculator puts it at 5 nanometres; one physics handbook says 10. It was meant for tiny distances, such as those inside computer chips. If you have a beard, it has grown about 20 beard-seconds while you read this paragraph.
The Jiffy: “In a Jiffy” Is a Real Measurement
When someone says they’ll be back “in a jiffy”, they’re using slang that dates back to at least 1780. But scientists have given the word real values.
In 1926, American chemist Gilbert N. Lewis defined a jiffy as the time light takes to travel one centimetre: about 33 trillionths of a second. In electronics, a jiffy is one cycle of mains electricity, 1/50 or 1/60 of a second depending on where you live. In computing, it’s often one tick of a computer’s internal timer, commonly 10 milliseconds.
So the next time someone promises to be back in a jiffy, ask them which one.
Units hiding in plain sight
Some weird units are so familiar that we’ve stopped noticing how odd they are.
Horsepower: A Sales Pitch That Stuck
The horsepower in your car’s specs started as a sales pitch. In the 1700s, Scottish engineer James Watt was selling his improved steam engine, but many buyers had no older engine to compare it with. They used horses. So Watt measured horses.
After studying a brewery horse in 1782, he settled the next year on 33,000 foot-pounds of work per minute, the same as lifting 550 pounds by one foot every second. One horsepower is about 746 watts, a unit named after Watt himself.
The funny part? A real horse can beat it. Horses can work at about one horsepower all day, but in short bursts they have been measured at almost 15.
The Size of Wales (and Other Countries Used as Rulers)
Read British news for long enough and you’ll see rainforest loss measured in Wales. Wales covers about 20,779 km² (8,023 sq miles), and “an area the size of Wales” has become a favourite way to describe forest destruction. A BBC Radio 4 programme about numbers even built a scale on it: a milliwales is roughly the town of Barry, and a hectowales is roughly Saudi Arabia.
A Welsh charity called Size of Wales has turned the joke around. It works to protect an area of tropical forest the size of Wales.
Other places have their own versions. Belgium is a popular yardstick for area, and Australians measure water in Sydney Harbours: one is about 562 billion litres, or roughly 238,000 Olympic swimming pools. Those pools are a unit too, along with football pitches and double-decker buses.
So, which weird unit is your favourite?
Most of these units started as jokes, but they stuck because they do something metres and seconds can’t: they make numbers feel real. Nobody can picture 10⁻²⁸ square metres, but everyone can picture a barn.
Would you rather measure your commute in smoots, your lunch in bananas or your next deadline in jiffies? Tell us in the comments.
Love facts that sound made up? Read our timeline facts that sound fake or explore the weird borders you can actually visit. And pin this one for the next time someone asks how long a jiffy is.