The British way to write numbers in words
British English has a firm convention that American style often skips: the word "and" sits between the hundreds and everything after them. So 342 is three hundred and forty-two, and 1,005 is one thousand and five. The "and" also appears when a big number ends in something smaller than a hundred, which is why 21,012 comes out as twenty-one thousand and twelve rather than twenty-one thousand twelve.
Two more rules do most of the remaining work. Compound numbers from twenty-one to ninety-nine are hyphenated (sixty-four, ninety-nine), while round tens are not. And when a number spans several groups of thousands, commas separate the groups in writing, mirroring the commas in the figures themselves.
The tool applies all of this automatically for anything up to 999,999,999,999, with decimals to two places. In normal mode decimals are read out digit by digit, so 3.14 becomes three point one four. In currency mode they become pence.
Worked examples
How to write a cheque
Cheques are rarer than they were, but when one matters (a deposit, a club subscription, a gift) it has to be right or the bank may bounce it. Write the date, the payee's exact name, the amount in figures in the box, and the amount in words on the long line. The words and figures must agree. Finish the words with "only", as in Seventy-six pounds and twenty pence only, and rule a line through any space left on the line so nobody can squeeze in an extra word.
There is a neat legal wrinkle here: under the Bills of Exchange Act 1882, if the words and figures on a cheque disagree, the amount in words is the one that counts. In practice most banks simply return a cheque with a mismatch, which is exactly why copying the words from a converter beats improvising them at the kitchen table.
Currency mode follows cheque conventions: a capital letter to start, pounds before pence, "and" between them, and "only" at the end. Amounts under a pound come out as pence alone, so £0.45 reads Forty-five pence only.
A billion is a thousand million
British English once used the long scale, where a billion meant a million million. That meaning was retired from official UK use in 1974, and modern British English matches American usage: a billion is a thousand million, and a trillion is a thousand billion. This tool uses the modern short scale, so 999,999,999,999 is nine hundred and ninety-nine billion, nine hundred and ninety-nine million, nine hundred and ninety-nine thousand, nine hundred and ninety-nine.
Everything runs in your browser and nothing you type is uploaded, so the tool is safe to use with invoice amounts and other figures you would rather keep to yourself.
Frequently asked questions
How do you write 105 in words in British English?
One hundred and five. British English puts an "and" between the hundreds and whatever follows, so 342 is three hundred and forty-two. American style usually drops the "and".
When do numbers need a hyphen?
Compound numbers from twenty-one to ninety-nine take a hyphen: twenty-one, forty-seven, ninety-nine. Round tens do not, so forty and ninety stand alone. The hyphen also survives inside bigger numbers, as in three hundred and sixty-five.
What is the largest number the tool can convert?
It handles whole numbers up to 999,999,999,999, which is nine hundred and ninety-nine billion and change, plus decimals to two places. That comfortably covers cheques, invoices, legal documents and homework.
How do I write an amount in words on a cheque?
Tick currency mode and copy the result, for example One hundred and five pounds and fifty pence only. Write it on the long line, make sure it matches the figures in the box, and rule a line through any leftover space so nothing can be added.
Is a billion a thousand million or a million million?
In modern British usage a billion is a thousand million (1,000,000,000), the same as in America. The older British long scale billion of a million million fell out of official use in 1974, and this tool uses the modern meaning.