Last updated 3 September 2026
Where written numbers still matter
Writing an amount in words is a safeguard rather than a formality. Digits can be altered with a stroke of a pen; words cannot be extended without it being obvious. That is why cheques, contracts and formal invoices carry both, and why the two are expected to agree exactly. The wording conventions differ by region in one small but persistent way: British English inserts "and" before the final part of a number under a thousand, so 105 reads "one hundred and five", while American English writes "one hundred five". Neither is wrong, but mixing them within one document looks careless, so the style is selectable here.
Where written numbers are required
The main reason this conversion matters is fraud prevention on financial documents. A cheque carries the amount twice — in figures and in words — because a figure can be altered with a single stroke of a pen while a written amount cannot be. In most banking practice, where the two disagree, the written words are the legally binding version. The same logic drives written amounts in contracts, invoices and legal filings.
The convention for currency is to write the whole units in words and the fractional part as a numeral over 100, which is why cheques read like Four thousand two hundred and fifty and 37/100. Some institutions also expect the line to be closed with a stroke or the word ONLY so that nothing can be appended afterwards.
British and American conventions differ
Two differences catch people out. British English inserts and before the final part of a number under a hundred, giving one hundred and twenty-five; American English drops it, giving one hundred twenty-five. On a formal document, follow whichever convention the receiving institution uses.
The larger difference used to be the meaning of billion, which historically meant a million million in British usage and a thousand million in American. British usage has followed the American definition since the 1970s, and it is now standard in UK government and financial reporting — but the older sense still appears in historical texts and in some other languages, so a figure quoted from an old source is worth checking. Hyphenation is more stable: compound numbers from twenty-one to ninety-nine take a hyphen in both conventions.
Common questions
What is the difference between the British and American styles?
Only the word “and”. British English writes 105 as “one hundred and five”; American English writes “one hundred five”. The difference appears wherever a hundreds figure is followed by a smaller part.
How should an amount be written on a cheque?
Choose a currency above and the output follows the usual convention — the whole amount in words followed by the currency name, then the fractional part. Practice varies slightly by bank and country, so check anything unusual against your own bank's guidance.
How large a number can it convert?
Up to the quintillions, using the short scale where a billion is a thousand million. Beyond that, ordinary number handling loses precision, so very large values are declined rather than converted inaccurately.
Does it handle negative numbers and decimals?
Yes. Negatives are prefixed with “minus”, and decimals are read out digit by digit after “point” unless a currency is selected, in which case the fractional part is treated as cents or pence.
Why do cheques show the amount in both figures and words?
Because figures can be altered with a single pen stroke and written words cannot. Where the two disagree, banking practice generally treats the written amount as the binding one, which is why the words matter more than the numerals.
Should I write one hundred and twenty-five or one hundred twenty-five?
British English includes the and, American English omits it. Both are correct within their own convention, so follow whichever the receiving institution uses. Compound numbers from twenty-one to ninety-nine take a hyphen in both.
Does billion mean the same thing everywhere?
Now, largely yes — a thousand million. British usage historically meant a million million and shifted to the American definition during the 1970s. The older sense still appears in historical texts and in some other languages, so old sources are worth checking.