Working with numbers

The figure 0

This is usually called nought in British English, and zero in American English.
When we say numbers one at a time, 0 is often pronounced as oh. e.g. "My bank account number is six two oh four eight." (62048)
When measuring temperature, 0 is always pronounced as zero. e.g. "Zero (0) degrees Celsius is thirty-two (32) degrees Fahrenheit."
0 scores in games are usually nil in British English, and zero or nothing in American English.
e.g. UK commentator -- "France beat Brazil three -nil (3-0) in the World Cup Final."
US commentator -- "France beat Brazil three to nothing in the World Cup Final."

Telephone/Fax numbers

Native speakers usually say each number separately, with a pause after every three or four numbers. e.g. "oh (zero)-seven-eight nine-nine-two five-five-one-nine" (078-992-5519)
If the same figure is used twice, in British English we usually say double. e.g. "My telephone number is double nine one, double five oh seven." (991-5507)

"And" punctuation

In British English, native speakers always use and before tens in numbers. e.g. "We sold three hundred and sixty (360) machines last year."
Some American English speakers would say: "We sold three hundred sixty machines last year."
When expressing measurements using two different types of units, and is optional. e.g. "The plane will arrive in two hours (and) thirty minutes."

Using "a" and "one"

We can use a at the beginning of a number, instead of using one. e.g. "A/One thousand and two" (1,002); "The train will leave in an/one hour and fifteen minutes."
"A thousand" can be used, but usually not before a number with hundreds. e.g.: "One thousand, five hundred and twenty."(1,520)
Using a is generally more informal than using one.

Thousand/million/billion etc.

The number 1,999 is expressed as "One thousand nine hundred (and) ninety-nine."
The year 1999 is expressed as "Nineteen ninety-nine."
The year 2000 is expressed as "The year two thousand."
The year 2001 is expressed as "Two thousand and one."
The year 2013 is expressed as "Twenty thirteen." or "Two thousand and thirteen."
165,000 is expressed as "A hundred (and) sixty-five thousand."
1000,000 is expressed as "A million."
1000,000,000 is expressed as "A billion."
NB British English used to express 1000,000,000 as "A thousand million" but "A billion" is now the accepted international usage.
1000,000,000,000 is expressed as "A trillion."

Twelve hundred etc

In informal speech, we often say "twelve hundred" (1,200), instead of "one thousand two hundred".
This is mainly used for numbers between 1,100 and 1,900.

Using numbers as adjectives

Numbers can work like adjectives, and are therefore singular, when used before a noun to describe quantity. e.g.: "He bought a two-million-dollar house in Australia"(NOT two-million-dollars); "My new laptop computer has a 14-inch screen"(NOT 14-inches); "It's a twenty-minute walk from here to the station."(NOT twenty minutes)

Describing areas

To describe the size of an area, or room, we use by, e.g. "The room measures three metres by five metres."
To describe a cross-sectional area we also use by, e.g. "The house was built with two-by-four (2 x 4) timber."
An area measuring, e.g., "four metres by four metres", can be expressed as "four metres square".

Using "a" and "per"

When relating two different measures, we usually use a/an or per. e.g. "The room charge is one hundred fifty dollars a night."; "My car's top speed is two-hundred and ten kilometers per hour."
Per is used more often in formal writing.

Money/Interest

When talking about exchange rates and foreign currencies, we usually use the following structure: "How many yen are there to the dollar today?"; "There are currently one hundred and fifty yen to the dollar."
Interest rates are expressed in terms of "per cent" e.g. + 0.5% is expressed as "An increase of a half of one per cent."

Time Expressions

In informal speech 14:15 is expressed as "(a) quarter past two" by British English speakers and "(a) quarter after two" by some American English speakers.14:30 is expressed as "half past two" in both cultures.14:45 is expressed as "(a) quarter to two" in both cultures.
In more formal speech 14:15 is expressed as "two -fifteen",14:30 as "two-thirty" and 14:45 as "fourteen forty-five" in both cultures.
For announcements about travel schedules at airports and train stations the 24-hour clock is used. 14:15 is expressed as 'fourteen-fifteen', 14:30 as 'fourteen-thirty' etc.
HOWEVER, 14:00 is expressed as 'fourteen hundred hours' or simply 'fourteen hundred' when it is announced over a PA system.