UK also uses mph, so this should not bother the questioner.

12:01 AM is just after midnight (00:01). 12:01 PM is just after noon. There is no ambiguity on this point. And no one in the US uses stones for anything at all; that's the UK that uses them.

@cpast Then it is 11:59 a.m., 12:00 (what ?), 12:01 p.m., 12:02 p.m.......12:59 p.m., 1:00 p.m. So the 12 occurs before the 1 and if I mention that, the americans are getting unsure themselves.

And it gets worse. The new day begins at midnight, but the clock runs continously, indicating no break, so 11:59 - 12:XX runs one hour into the new day. Example: We meet at New Year's Eve at 12:02 p.m. I say: Lets meet us again at 12:48 p.m. Do we meet in 46 min or in 1 day 46 min ?

12 PM generally means noon, and AM means midnight. In your example, you mean 46 minutes, just like "let's meet at 2:39" doesn't mean "meet tomorrow." And again, 12:02 PM is unambiguously the afternoon, not early morning. It's really not very complicated.

While purists claim 12 AM or 12PM is not well-defined, in practice a clock saying "12 AM" means midnight.

"1 gallon = 4,5 l (important for filling the car" -- actually it sort of isn't important. You never actually need to know how much a gallon is compared with a UK gallon, you just need to know how fast you're using fuel and how much it costs to replace it. If you brought your UK car with you to the US, then it'd be useful to convert you knowledge of that car to the units you'll buy fuel in, but that's not usually an option.

Been an American all my life, we don't use stone, and I've never heard of a hundredweight. I thought these were British terms.

@cpast I am absolutely certain that I saw stones in the US, is it perhaps used for boxers or martial artists ? I removed now the section because I am now unsure myself.

Oh and most cars in the US have kph under the mph on the speedometer.

Realistically, I don't think you should be computing braking distances while driving or need to know exactly how much a gallon is. Just fill up the tank when it's running low… I also admit that I am a bit confused by this 12 AM/PM thing but pretending that Americans “still” use them without knowing which is which is patronising and unnecessary.

"1 gallon = 4,5 l" -- this is the definition of a UK gallon. In the US, a gallon is 3.8l. Also, I've lived in the UK my whole life and have never once heard anybody use a quart as an actual measurement. And the metric equivalent of a ton is spelled "tonne" in UK English.

Another important car-related conversion for the OP is of course: left lane = right lane and vice versa :)

If you're going to cook, you should find out what a "cup" is, I think around 240 ml. By the way, doesn't the UK use 12 hour clock as well?

@AndreKR It's not like we use one or the other exclusively. If you have a physical, non-digital clock (i.e. one with hands and a mechanism) then it's probably going to be a 12 hour clock; you were probably taught how to tell the time using one as a kid, too. Digital clocks, computers, phones, etc. can generally be set to whatever you prefer. Also, "cup" is a standard measurement in the UK too, it's just less widely used; you can buy a set of measuring cups in places that sell cooking utensils, including most supermarkets.

One further thing to bear in mind on the road: British warning signs for things that are about to happen (e.g., roadworks, exits, lane closures and so on) are in yards or quarter-miles; the equivalent American signs tend to be in (thousands of) feet.

@DavidRicherby I only see hundreds or thousands of feet when I'm under a quarter mile; exit signs on roads I travel typically have a sign at the previous exit (with however many miles it is), a sign 2 mi. out, and then a few more signs as you get closer, at say 1 mi., 1/2 mi., 1/4 mi., and then maybe something at 1000 ft. or 800 ft. particularly if the exit comes up suddenly/isn't visible at that distance/whatever. My driving is all northeast, though. Though I will mention that the signage in New Jersey is awful (why would you ever put a sign for an exit after the exit?!).

Dodgy rounding! 100kph = 62mph - so on your suggestion of 65mph, I'm speeding.

@OllieFord This is for someone coming from kph to mph. I'm fairly confident that no road anywhere in the United States has a speed limit of 62 mph. 60 mph, sure. 65, that's pretty common on highways. 62, no. So, if the OP sees a 65mph speed limit sign and goes at 100kph based on this answer, they aren't speeding (they're going a bit too slow, actually). In practice, of course, an American rental car's speedometer reads in MPH, which you'd use when comparing against a speed limit (the conversion is more "what does this speed feel like")

Oh. I forgot the USA used mph too. In that case, there's no conversion necessary. We use mph in the UK too. My point was not that signs say 62mph, but that in Europe they may say 100kph; in which case if you only have an mph dial (older car) then you should stick to 60 in such a zone, 65 would be speeding. But regardless, no conversion necessary for OP.

@OllieFord Still no speeding. In Europe it is mandatory to have speedometers which show a slower speed than actual, so speedos here are something like 105%/110% of actual speed. The police have tolerances which are mostly something like 10% to avoid measurement errors.

I can't think a use for knowing ton when on holiday, but a ton (uk) \= ton (us) \= tonne (metric), the uk uses the metric...

When I went by car last year in Pennsylvania (as a passenger), at some points we went about 5 mph over the limit speed, and lots of cars passed us quite fast (i.e. by at least 10 more mph). I don't buy your prohibitive punishments in general (though it might depend on the state).

@PaŭloEbermann I think you are conflating two things: The issue when the police thinks you are speeding (they can be lenient or strict) and what punishment you can get if they are convinced you are speeding. You can drive 90 mph and nothing happens when in fact you are simply lucky and/or the police is lenient. And you can drive 57 mph and meet an ultra-strict policeman in a strict state. The USA consists of 50 states, some lenient (North Dakota), some draconian (Virginia) and if the sheriff said it's speeding, it's speeding. You simply don't want risking your journey.

Addition: The law in a state can change always and mostly not in the lenient direction. In Virginia going over 90 mph gives you very probably jail time. 25 years ago when I was the first time in the USA, we three were in fact caught on our way from Cal. to Wash. and it would have been over for us. I was driving two years ago in Poland on idyllic, small roads and was regularly overtaken by natives with more than 20 kph(12 mph) than the speed limit. Is that a reason to assume you may drive as fast ?

On the 12 AM/PM issue: if the time is exactly 12:00, it's common to describe it as "12 noon" or "12 midnight" and avoid the whole "is noon 12 AM or 12 PM" mess.

also note when checking the fuel consumption of a car, while both UK and US use mpg, the "gallon" therefore the fuel consumtion will be different in the UK mpg and US mpg

What happens if they catch you speeding?

@Joze In our standard case it was a civil car with a radar gun which our driver kindly overtook. We were talking and so he slipped into standard German speed (130 kph = 85 mph) on a 55 mph road. Standard procedure: Lights on, driving behind us, we pull off the road, he stops behind us, our driver puts the hand on the wheel (Don't go out). Driving license, car docs. He will inform you how bad it is (fine, confiscation) and in our case it was pretty bad. He was letting us off the hook, but he had us and he knew it. So I have burnt fingers and I am not completely objective.