One of the things you notice when moving to the US from another country that America uses its own units of measurement for everything, e.g. miles and feet for distance and length, pounds for weight, Fahrenheit for temperature, instead of the metric units used almost everywhere else. According to Wikipedia – Metric system, the only remaining countries that don’t use the metric system are the US, Burma/Myanmar and Liberia
People often make fun of Americans for being almost alone using its historical legacy units instead of using the system that is accepted by the scientific and international community. To their defense, there is actually nothing wrong with their units, they are well defined and serve them well for decades (centuries?). Just like it’s annoying for people who’s never been in the US to use the US units, it’s also difficult for Americans to use the metric system, so why switch?
All this aside, do American or international units have advantages over each other, other than just being more familiar in their users’ mind? Here’s what I think
Fahrenheit vs Celsius
This is probably the hardest to adapt to, because the conversion involves both addition and a multiplication, e.g. to get the Celsius representation of 70F, you need to subtract 32 then divide that by 1.8.
Ont the other hand, this is probably the easiest to pick a winner. For expressing indoor or outdoor temperature, I think Fahrenheit definitely wins. We can think of range 0-99 as the prime range, because you can use two digits easily in conversation without resorting to decimal points. In Fahrenheit, this range almost map perfectly to the range of possible temperature, 0 being as cold as it can normally get and 99 being the upper bound. Firstly, this means you don’t have to resort to negative numbers or 3 digits. Secondly, it optimizes the resolution. 50’s, 60’s, 70’s, 80’s, all have their own feel. Compare with Celcius, saying 10’s or 20’s is not specific enough, while saying 18, or 27 is too specific to say without basing on accurate info.
Miles vs kilometers
Miles and kilometers are easier to convert than Celsius vs Fahrenheit, they have a constant 1 mile = ~1.6 km proportion. Which one is better I think depends on the way you travel. For example, in the Bay Area (except urban area like SF), driving on freeways is the most popular way to get between places. The freeways have 65 miles/hour speed limit, so 1 mile/minute is a good approximation of average speed. This means mile is a nicer unit to have because it can be use to directly estimate travel time, so when something is say 40 miles away and you get there using freeway, 40 minute would be a good estimation. On the other hand, in places like Sumatra, Indonesia, for intercity travel 60 km/h is a decent average speed, so probably kilometers would be better. And most trips will be within city anyway and your speed is normally somewhat less, dictated by traffic condition and stuff like that.
Kilograms vs pounds
I don’t see any clear advantage. They both convey their meaning, e.g. saying something is x kg is as clear and useful as y lbs, as long as you’re familiar with it. Probably pound is a little bit confusing because it’s subdivision is not decimal (1 lb = 16 ounces). Also there are competing systems of mass with the same terminology (e.g. troy pound and troy ounce), with somewhat different definitions. But you rarely encounter this in daily life.