US and UK style
The two styles differ in one word. British English puts "and" after a hundred and before a final part under 100 — one hundred and twenty-three, one thousand and five — while American usage normally leaves it out: one hundred twenty-three, one thousand five. Both hyphenate compound numbers from twenty-one to ninety-nine. Negative numbers are written with "negative" in US style and "minus" in UK style.
Large numbers use the short scale, where each new name is a thousand times the last: a billion is 109, a trillion 1012, a quadrillion 1015 and a quintillion 1018. This is standard in modern English in both countries; the older British long scale, where a billion meant a million million, is no longer used in official figures.
Decimals and ordinals
Digits after a decimal point are read one at a time — 3.05 is three point zero five — because that is how they are spoken. Ordinal numbers (first, second, twenty-first, one hundredth) describe position rather than quantity, so they are only produced for whole numbers of zero or more; the figure with its suffix, such as 21st, is shown beside the words.
Writing a cheque
On a cheque the amount is written in words so that it cannot easily be altered, with the cents or pence as a fraction of 100: One thousand two hundred fifty dollars and 75/100. Some people write "and 75/100 dollars" or add "only" at the end; the convention varies, and the amount in words is generally what counts if it disagrees with the figures. The converter also gives the amount fully in words — one thousand two hundred fifty dollars and seventy-five cents — for contracts and invoices.