More or less all measurement systems in the US varies from what is used in Europe.
Distances and speed are measured in miles, yards, feet and inches.
12 inches to a foot,
three feet to a yard, and
5.280 feet to the mile, which is 1.609 meters.
Very logical and easy to remember?
For a fast conversion 4 inches are app. 10 cm., 1 foot app. 30 cm. In writing the notation is an inch=1” and a foot=1’.
Note that this also applies to tools. Hex-keys and screws are measured in x/8".
Volume is measured in oz. – ounces – cups, pints, quarts and gallons. 128 ounces/16 cups/8 pints/4 quarts per gallon, or converted to metric 3,78 liters.
Weight is measured in pounds and a different kind of ounces, 16 oz. per pound = metric 454g.
Temperaturers are not measured in Celcius but in Fahrenheit, where water freezes at 32F and boils at 212F.
C = 5/9 x (F-32),
F = 9/5C + 32.
Also a straight forward conversion?
Time. Fortunately a minute is still 60 seconds and an hour 60 minutes, but the day is divided in two times 12 hours, a.m. and p.m.
A.m. means ante meridiem, latin for ”before noon”, and p.m. is post meridiem, after noon. Midnight er not 0:00 but 12:00 a.m.; noon should rightfully be 12:00 m, changing to 12:00:01 p.m. a second later.
The 24-hour system is only used in the military where they can't afford mistakes. Everybody else has at some critical time set the alarm clock for p.m. where it should have been a.m.
Denotation of Dates is mm/dd/yy - New Years Eve 2012 will be 12/31/12, and particularly for dates early in the month this can create some confusion. You are probably not in doubt that 31 is not a month but is 07/04 Independence Day or April 7th?
If communicating across the Atlantic you better get used to using Apr, Jul, and the other abbreviations.
Just to add to the confusion the weekend is not at the end of the week. The week starts on Sunday and ends on Saturday in the calendars.
A consequence of this is that the number of the week may be different between Europe and USA. If the year ends mid week it becomes week 53 or 1 depending on which part of the week has four days. So if January 1st is a Thursday it will be week 1 in Europe and week 53 in USA. The number is rarely used, at least not in California, and most calendars are not prominently marking the number, so when family members tell me that their vacation in is week 28 I frankly don't know exactly when they are likely to be away and can't plan a trip to the old country using the information.
Daylight savings time doesn't change the same weekend either, so for a couple of weeks in spring and fall the time difference between Europe and the US is changed. For very early morning or late night telephone calls I do apologize - I can never remember if my extended family is 8 or 10 hours away during those weeks.
The seasons change on solstice and equinox, not like I was taught as a child on Mar, Jun, Sep, and Dec 1st.
In mathematics the decimal sign is a punctuation mark and the 1000 separator is a comma - totally opposite what I have been used to. A pound is 0.454 kg, and a mile is 1,609 meters.
The electric current is 110V and the outlets have rectangular holes, so you will probably need to get new appliances and tools. For more on appliances etc. see Housing.
When you print a piece of paper it will be letter format, shorter and wider than A4 and the binders for archiving have three holes, not two or four. The paper may also be in the also common legal format, 1.333 as long as letter format and, hence, very difficult to archive.
For someone growing up metric this is all very cumbersome and hard to learn. You quickly learn that 72F (22C) is a pleasant temperature and setting the oven at 400F when your food needs 200C; but when the doctor asks your son's temperature? How tall your child is?? His weight?!? The medical world claims to have gone metric but I have yet to see it practiced.
You may know that the currency of USA is dollars and cents, but then the Americans start talking about pennies, nickels, dimes and quarters. These are the common names for the 1, 5, 10 and 25 cent pieces. Although many financial transactions happen using a credit card, you still use cash like quarters for parking.
The biggest common coin is the quarter even though you may see a halfdollar or a dollar coin. Most one dollars are still paper bills even though the value is less than one Euro.
Phone numbers have the format 1 (aaa) nnn-nnnn.
1 is USA's country code. It is also Canada's country code. When telephones systems developed over 100 years ago (here before it happened in any other place) they thought that they would never run out of numbers, so Canada could have a part of the number series. That was naive.
The area code is 3 digets (aaa), and the individual number is the last 7 digets. You don't need to dial the area code if you are calling from within the same area, but if you dial outside of your area you have to dial the country code first. It is not prominently written anywhere in your phone book but if you don't remember the 1 you will be told that the number doesn't exist. Fortunately many phones know to enter this automatically, but not all, and if you save a 7 digit number in your mobil phone remember to ask for the area code as well.
If you are calling from a normal phone you need to dial 011 to get a line out of the country - on the mobil phone the +sign does the job.
(I am fully aware that on modern telephones dialing is now replaced with entering but in common speech - even among teenagers - the term dialing is still used for making a call.)
Many companies have chosen their phone number so the letters that corresponde to the numbers make an easy to remember word. 1 (800) FLOWERS will be happy to help you with a floragram. Calls to 800 numbers are paid by the receiver. Most numbers in the 900 series will cost a lot of money on your telephone bill. The exception is 911 – Emergency. 411 gives you number information and 511 the latest traffic updates.
Radio and TV
If you are driving and don't want to use your phone you can instead hear traffic updates on National Public Radio stations (npr.org) that also cooperate with BBC Worls News. NPR gets just as many complaints about their programs from the left and right of the political spectrum - an indication that they are not as biased as many other stations. (In the Bay Area the station KQED kqed.org carries NPR's news feed along with local programs.)
Many families use Tivo, a system where you can screen out the many advertisements that make television shows twice as long as they need to be.