I remember back in the 3rd grade (about 1978) my teacher saying that the United States would be going to the Metric system exclusively just like Canada (and most of the world) uses.
Question: Why do we still use the standard system, along with metric equivalents in some cases, instead of the Metric system exclusively? Did something occur that changed the plan?
Nothing changed. The plan is still there.
What you didn’t notice is that the plan recommends that Americans should use the metric system, and that there was nothing to require any American to use the metric system.
Inertia wins again.
Yeah. Massive resistance.
People just didn’t like the idea of adapting to a different system for everyday use. The same thing is happening now in Britain, not only with respect to weights and measures but also to currency.
In the U.S., there has been fairly broad conversion to the Metric system in the industrial sphere. Automobiles, for examples, use Metric hardware. Companies that deal in international trade saw that clinging to the British/American system would hamper and hurt their business, so they changed over.
But for internal U.S. business, e.g. at the grocery store and the gas pump, the public largely eschewed “metrification,” not seeing any compelling reason to embrace it. The government finally gave up trying to push it.
A lot of common words and expressions would become meaningless:
Mileage (what would we call it, kilometerage?)
Foot-long hot dogs, what would we call them then? And what about inchworms?
Dieters would no longer see if they could still “pinch an inch.”
“If I walked a mile in your shoes…”
“An ounce of prevention is worth a pound of cure.”
Denver’s moniker as the “Mile-High City” would mean nothing.
You get the idea.
As has been mentioned the real written-down plan never changed, it was just a recommendation. As for why the recommendation was never followed, that’s two reasons:
The people saw no benefit to it. The US Standard system, for all its irrational design features, works. If people can learn a language from childhood, they can learn and use just about any measurement system from childhood. There is nothing magically perfect about decimalization, and decimalization is the ONLY thing somewhat unique that the SI has going for it. There is nothing magically inherent in any of the SI units.
Second, the way it was presented was about the worst possible way to do so. I recall tedious time spent in school learning to “convert”. Thus, people associated “metric” with “lots of stupid math I now have to do instead of getting on with things”.
In any case, there’s no overriding need to adopt it. The USA’s economy is large enough so that we do just fine without. Problems only arise when somebody tries to MIX the two systems.
And sometimes not even then. The soft drink companies seem to be doing very well with 2-liter bottles and 12-ounce cans.
So did other countries that are now fully “metricized” (is that a word?) go through the same growing pains of conversion, or were they always metric (or some close relative of it)?
dwc1970 - Like those answers! 
Nah. We went metric ages ago, and still use the old words in aforisms and stuff. Lumber is still sold as 2x4, meaning inches, not centimeters. Same with nails, screws, bolts and stuff.
Oh, and in Europe, gas milage is expressed as liter/100km.
Magical might be a strong word, both the thing about the conversions is that not only is it nifty to just move the decimal comma around, it’s easy to convert in other ways:
1x1x1 meter = 1 cubic meter = 1 ton (of water)
1 decimeter (10 centimeters, 0.1 meter)^3 = 1 liter (of water).
Back in '85, when I studied in the US, there where roadsigns for the speedlimit, which were both metric and the other way. It would say: “55 mph” and “88 km/h”. I fully understand how metric would seem utterly stupid, seeing it like that. Had it been posted as “90 km/h” it would not have been so hard. It’s close enough for that purpose and gives a nice round figure, easy to see and remember.
A lot of the conversion stupidity is like that, but I understand what you huys mean: You have a feeling for what 80F is. To state the same temperature in C would be meaningless, as is F for me.
So the Americans don’t want the change. I think it’s your loss, since metric is so much easier. YMV obvbiously.
You must have meant YKMV 
Sorry, couldn’t resist it…
Dan Abarbanel
Up in the Great White North, the metric system is officially used as the exclusive measuring system. However, I have no idea what my height and weight are in metric, litres/100 km means nothing to me, and paint is still sold in gallons (although they’re labelled 3.89 litres). As part of that generation that grew up during the convertion, I’m still fairly comfortable with inches, feet, pounds, quarts and gallons. I can guesstimate farenheit, but have little concept of what miles are. Since football fields are still drawn with yards, rather than the slightly larger metre, I still know what they are as well.
So, to sum up, we’re still in transition in many ways, even 25 years later.
P.S. I really get a kick out of how sci-fi shows always use metric measurments to sound “hi-tech” and “futuristic.”
All these sayings (apart from the mileage) would probably survive as they are, as they had in french. I doubt a lot of french people would had a clue what a “lieue” an “once”, a “grain”, a “chopine” or a “maille” could be, but they will understand the meaning of common sayings which include these words.
What happened is, in those cases, the State forced the matter, adopting the “metric” (and later SI) as the only officially recognized system of measurement.
In the UK, daftly draconian measures were instituted. It is a crime to sell all but a few goods in the UK using English measures.
Since the metric system was an artificial creation, every country had to adapt to it at some point. Even in France, though it was designed under the revolution and the empire, it wasn’t made mandatory before the middle of the XIXth century, and it took longer before former units actually completely dissapeared from common use.
Some former units are still used in name, but now actually refer to a metric measurment. For instance, one can still buy a “stere” of wood or a “livre” (pound) of apricots, but what people actually mean is a cubic meter and half a kilo, respectively, which are relatively close approximations of the former stere and livre.
My grade school years were in the middle of the “change over”. I was taught the metric system but not English Standard.
I’m somewhat pissed the US didn’t convert because I know nothing about English Standard.
I don’t know how many tablespoons there are in a pound, how many inches in a gallon, or how many fathoms in a ton.
I can order a pint though.
Not quite. It also avoids the ambiguity between force and mass. And it is without the confusion between
• Statute miles, Survey miles, Nautical miles
• Troy ounces, apothecaries’ ounces, ounces avoirdupois
• Troy pounds, apothecaries’ pounds, pounds avoirdupois
• Imperial gallons, US gallons (ditto for pints)
I know those aren’t used much by ordinary people for everday purposes. But they do cause problems and you said ‘the only advantage’.
Decimalisation may not be magical, but it beats the hell out of trying to deal with the conversion factor between barleycorns and rods (2376), or between drams and hundredweight (12800 in the US, 14336 in the Empire, whereever that is). The English Mediaeval system has nothing going for it.
Regards.
Agback
As has been stated above, the other advantage of the metric system is that there is smoother transition from one type of unit to another.
As an engineer, I can’t tell you how often I do calculations like “One liter of water will have a mass of one kilogram and fill a cube 10 cm on each side.”
I just wish they had decided that a meter was “one fifth of how far an object will fall in a vacuum at sea level in the first second of freefall” because then g would equal 10 instead of 9.8
To follow up on Agback’s post, the force/mass ambiguity causes serious problems with the traditional system of units used in the U.S., especially when compared to the SI system.
The traditional system of units used by U.S. engineers is known as the U.S. Customary System (USCS). Unfortunately, in the USCS system of units, both force units and mass units are referred to as pounds. This makes complex problem solving absolutely hellish.
Check out what the National Council of Examiners for Engineering and Surveying (NCEES) puts in the intro to this handbook. (Note: PDF format)
You forgot the biggest one!
Vincent: you know what they call a “Quarter Pounder with Cheese” in Paris?
Jules: They don’t call it a “Quarter Pounder with Cheese”?
Vincent: No, they got the metric system there, they wouldn’t know what the f*** a “Quarter Pounder” is.
Jules: What do they call it?
Vincent: “Royale with Cheese.”
Jules: “Royale with Cheese.” What do they call a “Big Mac”?
Vincent: “Big Mac’s” a “Big Mac”, but they call it “Le Big Mac”.
Jules: “Le Big Mac.” What do they call a “Whopper”?
Vincent: I dunno, I didn’t go into a Burger King.