The US will never (i.e., at least for the next 50 years) change from the old UK units of measure (as locally implemented) to the metric system for three reasons:
(1) But it's HAAAARRRDD — There's always social inertia. People dislike change and the advantages of change in this case are perceived much lower than the cost (losing an intuitive understanding of measurements, looking stupid, etc.).
(2) Don't Tread on Me — We have a reflexively libertarian society. While one can chart out any number of exceptions, the US is not a top-down command-control nation. "The government" (in the US the federal government) cannot truly mandate adoption of the metric system, though it could certainly push the matter significantly. And, really, the issues in (1) can only be overcome by mandate and subsequent a generation of getting used to it. (That's both a bug and a feature of the American system.)
(3) America! — For too many people, use of American measurements has become somehow bound up in American heritage ("My grandpappy measured in ounces and Fahrenheit, so it's good enough for me!"), American exceptionalism ("Of course we use something different! We're better!"), American impudence ("The rest of the world can suck eggs!"), and the overarching sense of America as being the most important and powerful country in the world (see all the above). To propose changing to metric is not just to suggest an inconvenience (1) or the government treading on us (2), but to be positively un-American. It's to "give in" to those Europeans, or to the Chinese*, or to anyone else who isn't us. That can only be seen as a sign of weakness, of dependence, of the US not being able to dictate its own way, let alone the way the world operates.
In a sense, it's self-fulfilling prophecy: when America feels it has to change, it will be a sign that its importance in the world has significantly diminished.
There are a lot of reasons to change to the metric system. But until the reasons above are addressed, especially (3), it'll never happen here.
(*Though, to be fair, I expect at some point in time — when they feel they can mandate it — for the Chinese to introduce a decimaliized version of some traditional set of weights and measures. For their part, (1) is considered irrelevant, (2) is not the case as well, and this will be their version of (3).)
Why Americans still use Fahrenheit long after everyone else switched to Celsius
You can blame two of history’s all-time greatest villains: British colonialism and Congress.
Also, there is no value in day to day actions that makes metric better. 70 or 20 degrees out are both arbitrary numbers…and one isn't any more precise.
And the people who need to use the metric system do.
Try multiplying 2 yards 1 foot 5 inches by 3 yards 2ft 7 inches.
+Greg Stockton From a temperature standpoint, you're correct. Zero as freezing water is probably a minor benefit, but it is pretty trivial. The real advantages, from a day-to-day perspective, are the ease of using metric units and math.
And that (and to a lesser degree in temps) is where the inefficiency and risk of error comes up. Not only are non-decimal units a lot more difficult to operate with, but converting to and from metric (for the rest of the world) incurs costs (duplicate documentation, redundant tool sets) and the likelihood of making a mistake (of which the Mars Climate Orbiter is but one of the most prominent example; I've run into problems recently dealing with cabinet handles that are given in both metric and American units, but aren't completely interchangeable as such).
(1) is a bogus argument. The decimal system is the easiest for us to use!
Ask typical Americans how many feet are in a mile. Now ask typical non-Americans how many meters are in a kilometer? Which question receives the most correct answers?
But most Americans (those who don't remember from school, use the information, or live in Denver) don't really need to know the number of feet in a mile.
Ideally, it's easiest. Practically speaking, converting is harder than most people encounter in the hardness of the American system, just in terms of knowing what the hell a kilometer, meter, liter, centiliter, gram, kilogram, hectare, etc., actually looks / feels like. Vs. already knowing from decades of experience a mile, a yard, a quart, an ounce, a pound, an acre. The value is just not immediate or perceived.
+Scott Randel The problem is that we think in terms of the units we know, and we don't want to change, especially if it doesn't make things easier for us. (Unit conversion is MUCH easier in decimal, to be sure…but that doesn't come up as often as we think.)
If it's 20 degrees out, I grab a coat…I don't reach for sunscreen. When I'm cooking, I want my oven to be 350 degrees.
My daughter is 5'6"…I don't know how tall she is in centimeters…and as an aside, the "foot" is really good at measuring things between centimeters and meters.
My car gets 40mpg, and I drive 40 miles to work.
And while converting wouldn't be hard for me, and wouldn't be hard for many people, it's almost impossible to initiate the social change to make everybody do it, especially when there is so little value to them personally.
And here's an excellent example of the power of that social inertia: Metric time. At various points, people have tried to create a decimal based time system, which again would be much easier than our silly 60/60/24 measures.
So they try to create 100 seconds per minute, 100 minutes per hour, and 10 hours per day…or some variation on that theme. And those efforts have all failed spectacularly, because even though it would be easier in the long run, it goes against how people think.
There are two types of countries in the world. The ones that use the metric system, and the ones that put a man on the friggin moon 😉
+JD McCay As noted in (3). 🙂
Of course, people have accepted the metric system for one product: the 2-liter bottle of soda.
Oh, and kilograms for purchases of illegal drugs.
+Scott Randel Clearly if the US government used drugs, they would be able to convince people to convert to metric.
1979-80, BATF mandated wine and liquor be sold in metric-measurement bottles. A year later, Ronald Reagan disbanded the Federal Govt's metrication effort. Mere coincidence?