It’s an ongoing discussion – outside of the US -, around the question, Why in the world don’t the Americans use the metric system, like the whole rest of the world? Interestingly, inside the US, most people are unaware of such discussions at all.
One example of the importance of agreed units is the failure of the NASA Mars Climate Orbiter which was accidentally destroyed on a mission to Mars in September 1999 instead of entering orbit, due to miscommunications about the value of forces: different computer programs used different units of measurement (newton versus pound force). Considerable amounts of effort, time, and money were wasted.
On 15 April 1999, cargo flight 6316 from Shanghai to Seoul was lost due to the crew confusing tower instructions (in metres) and altimeter readings (in feet). Three crew and five people on the ground were killed. Thirty-seven were injured.
And in 1983, a Boeing 767 ran out of fuel in mid-flight because of two mistakes in figuring the fuel supply of Air Canada’s first aircraft to use metric measurements. This accident was the result of both confusion due to the simultaneous use of metric and Imperial measures and confusion of mass and volume measures.
To this day, the aviation world still uses the “US Customary Units”, as the US system of measurement units is called. The altitude of an airplane is expressed in feet, in the whole world, as far as I know, and I think the weight units are still pounds (Lbs), measuring for instance the amount of fuel on board.
Let me tell a little bit about my personal experience with the US system, and then I’m giving a simple answer to that question in the opening sentence.
During all the years when I was visiting from Germany to have mostly technical discussions with customers helping them to use our products, measuring units where a non-issue, simply because scientists and most science-related technicians use the SI (metric) system, almost without exception. I wasn’t aware of any problem with units.
That changed dramatically after we moved to Hilton Head. All of a sudden, people around us were talking like, isn’t it hot outside, 95 degrees again. Or: my son is growing so fast, he is already 5 foot 2. Or: I got a new car, with a gas mileage of only 20 miles per gallon, but the torque is 350 pound-foot. Or: try this recipe, you only need one tablespoon of butter and one teaspoon of sugar. I could continue this almost endlessly.
Can you imagine how my wheels were turning, after each such remark including US measurement units? Even if you are used to do the conversions into the metric system in your head, it always takes a few seconds away from your focus on the conversation at hand. Annoying! Or, you decide to ignore the conversion, leaving you without a clue as to what the other person meant.
Now I need to brag a little bit, as an opening gambit for a – what I believe – very important advice to all immigrants from metric countries (are there any others?). Very soon, after less than a few weeks into our new life in the US, I got so annoyed about myself not being able to immediately understand things that involved US units that I decided to develop the same kind of feeling that comes from using units you are familiar with. Like everybody in Germany has an immediate, almost physical understanding what 35 degrees means, or how long a half meter is, or how heavy 5 kg is, or how much 3 liters. I thought, there is no way I want to keep converting units in my head forever. I wanted to develop the same intuitive understanding of US units as a US-native, because everything else I tried wasn’t working.
It was easy! I just converted less and less in my head and accepted that, in the beginning, I only had a cursory idea about how much, for instance, 12.5 gallons is. Granted, it took quite a while. It was the easiest with temperatures. After a few weeks, I knew intuitively, without converting to Celsius, that for 50 degress outside I needed a sweater, 72 degrees was pleasant, and above 90 degrees it’s plain hot. The other units took a little longer to get accustomed to, but now I know immediately that a car with 20 miles/gallon is a guzzler, and 35 miles/gallon is good even by German standards.
Now, all in all, the “secret” is to mentally accept the sytem as it is and not to fight it like, why can’t they use the metric system? That’s my advice to everyone who stays here for more than a few weeks and plans to participate in the social life. Start thinking in US units from day one, like 70 is nice, 90 is hot, 40 is cold. Make your finger and your arms feel what an inch, a foot, and a yard is, and you’ll get the hang of it, very soon.
So, why don’t the Americans use the metric system, why didn’t they never even consider changing? Answer: Because they are happy with it, and the metric system does not really offer an advantage in the day-to-day life that people would recognize. That a foot has 12 inches is as easy to remember as a meter has 100 centimeters. Even in architecture, where we are so used to decimal scaling (like drawings in 1:100 scale), they use their system, scaling like foot:inch or yard:inch. When I had a new home built, I was poring over the architectural drawings that drove me nuts, initially, until I accepted their scaling, familiarized myself with it, and then, all of a sudden, it was as easy as the 1:100 drawings we are so used to.
It all comes down to our mindset!