Separation between hundreds and tens

Hundreds and tens are usually separated by ‘and’ (in American English ‘and’ is not necessary).

110 – one hundred and ten
1,250 – one thousand, two hundred and fifty
2,001 – two thousand and one

Hundreds

Use 100 always with ‘a’ or ‘one’.

100 – a hundred / one hundred

‘a’ can only stand at the beginning of a number.

100 – a hundred / one hundred
2,100 – two thousand, one hundred

Thousands and Millions

Use 1,000 and 1,000,000 always with ‘a’ or ‘one’.

1,000 – a thousand / one thousand
201,000 – two hundred and one thousand

Use commas as a separator.

57,458,302

The Number 1,000,000,000

In English this number is a billion. This is very tricky for nations where ‘a billion’ has 12 zeros. 1,000,000,000,000 in English, however, is a trillion.