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I am fairly sure that officially, the USA is metric and they have federally legislated conversion tables to accommodate those who don't wish to convert (everybody). No government has had the political strength to enforce a mass conversion of every measuring device yet.
Most corporations, particularly those that are international in scope, are metric. But everything that is sold in the states uses the imperial system only. With some exceptions, particularly building materials. There is no such thing as a 1/2" sheet of plywood anymore as the "half inch" sheet you buy isn't actually 1/2" thick. Same goes for all the other 'standard' thicknesses of sheet goods. That also goes for the dimensions of the sheets too (length, width). A 4' x 8' sheet is standard, but again, a 4 x 8 sheet isn't actually 4' wide by 8' long. I think that's because the sheet goods manufacturers have defaulted to metric measurements to be consistent with the rest of the world. The 'big 3' north american automakers (GM, ford and dodge) are also notorious for still using imperial components such as nuts & bolts, although they are starting to use more & more metric parts. But make no mistake, goods in their grocery stores are sold by the ounce & pound, fluid ounce, quart and gallon. You'll never see gas stations with signs displaying the cost of fuel per liter, either.
Canada switched to the metric system in 1975 or 76, and it was initially greeted with a LOT of resistance. For a couple of years, the price of fuel was displayed in both $/gal and $/liter just so that people could understand/see that prices didn't suddenly rise. To this day, goods in grocery stores are still advertised in both $/kg and $/lb. I was raised on the metric system, but I still internally convert km to miles when I'm driving. It just makes more sense to me. At 100 km/h (62mph), I cover 1 mile every minute. So if my destination is 250 km away, I convert that to ~150 miles = 2 hours, 30 minutes. When I started brewing, all the books available to me were written by americans. So when it comes to mashing & fermenting, I'm 100% fehrenheit. I know that a protein rest should be at about 122F, the sacch rest between ~142F - 158F, and mashout is at 167F. Lagers should primary at about 50F, lager at about 35-40F, and ales should ferment at about 65 - 75F. What any of those temperatures is in celcius, I have no idea. But I know that today's high was 11C and it's going down to about -2C overnight. I have no idea what those temperatures are in fehrenheit, though.
