Wednesday 6 February 2019

What's a gallon?

A little while ago, I wrote a post on Facebook complaining that my new car's fuel efficiency gauge was expressed in miles per gallon. "What's a gallon?" I asked.

Over here in England, fuel has been sold by the litre for decades. Gallons are an archaic unit which no-one under 40 has ever had to deal with.

Unitary council

Two friends very helpfully commented with conversion rates. "3.78 litres in a gallon" said one friend. "4.54 litres in a gallon" said another. While both answers were significantly different, both my friends were equally quite correct.

One figure is for a United States standard gallon, while the other is for an Imperial standard gallon. Which one does my car use?

"They went metric without telling us!"

"The car was made for the English market - It'll be the gallon that's used in England."

But we don't use gallons in England and we're back where we started. It could just as easily be argued that it probably uses the American gallon because that is the only unit called a "gallon" that is still in active use in 2019 and you can't say that about the imperial gallon. (Unless maybe Liberia or Myanmar still uses it.)

But this all misses the point. The gallon has inserted itself into the process quite unnecessarily. The car's electronics already tracks fuel levels in litres and would have to perform a calculation in order to show me fuel efficiency in gallons. That leaves me having to perform the opposite calculation to get the figure back into litres again. If the car designers had stuck with litres and didn't bother with pointless calculations, we'd all be a lot happier.

"I would walk 500 miles..."

"But Bill, you want to measure fuel efficiency in miles per litre, but why not kilometres per litre?"

While England have moved on from gallons, we remain tied to miles, regretfully. Speed limit signs are in miles per hour, as are the big numbers in my car's dashboard. I would love it if we joined the rest of the world and completed metrication. Our painless move from gallons shows we can do it.

Imagine if a filling station got it in their heads to start selling fuel by the gallon, as if it fell through a time vortex. Anyone stopping at that station is only going to ask "What's that in litres?". Most people would drive on, looking for a filling station that isn't weird.

Our move to litres is a success story for England. We can make the switch. We barely noticed when food and drinks (other than in pubs) started being sold by the kilogram or litre. We got used to it as we joined the rest of the world. A few people grumbled but the rest of got on with our lives. Switching to kilometres on the road will be the same.

Picture Credits...
"The Price You Pay" by Damian Gadal. (CC)
"They went metric..." by me!


  1. That table is designed like that to allow folks in a wheelchair to use it.

    Also, most cars have a setting that allow you to switch between MPG and L/100km.

  2. It's "litres" and "Britian" over here actually.

  3. 8 pints to a gallon. Britain may claim to be metric, but you still drink in pints, and in terms of driving, distance is still in miles. But "miles per pint" invokes the wrong connotations and "miles per liter" is just simply too odd to think about.