Reference

12 short pages, each answering one question. The answer is under each title below, and every guide links to the tool that does the same job, so you can read the rule or skip it.

Written 28 September 2026.

• How to write numbers in words Spell out numbers under ten in running prose, never start a sentence with a digit, and put a hyphen in every compound from twenty-one to ninety-nine.
• British and American number formatting British English says one hundred and five and American English says one hundred five. That one word is the whole difference, and neither form is a mistake.
• Cardinal and ordinal numbers An ordinal changes only the last word of its cardinal, so twenty-one becomes twenty-first. Seven are irregular: first, second, third, fifth, eighth, ninth and twelfth. The tens change y to ie before the th, from twentieth to ninetieth.
• How to write large numbers Mark a long number off in groups of three digits from the right, then say the groups from the left, each followed by its scale word except the last. The scale word stays singular: two million, never two millions.
• The long and short scale A billion is a thousand million in modern English. In British writing from before the mid-1970s it can mean a million million, so an old figure is worth checking.
• How Roman numerals work Seven letters, added from left to right, except that a smaller letter in front of a larger one is taken away. The standard form stops at MMMCMXCIX, which is 3,999.
• Common Roman numeral mistakes Ninety-nine is XCIX, not IC: in the standard form only I, X and C are subtracted, and only from the next two values up. IIII on a clock face is an older convention, not an error.
• How to write money in words The amount, then the currency, then the cents after “and”: one thousand five hundred rand and fifty cents. Rand takes no plural, and a pound has one penny but fifty pence.
• What the style guides say about numbers The guides agree on writing out a number that starts a sentence and on commas in long numbers. They split on one to nine, on millions, on the order of a date and on how to write a range.
• Place value explained A digit is worth its face value times its column. In 4,507 the 5 is worth five hundred, and the 0 is there to hold the tens column open.
• Expanded form explained 4,507 expands to 4,000 + 500 + 7. Standard form means 1.5 × 10³ in a British classroom and 1,500 in an American one.
• How to write decimals in words Said aloud, the digits after the point are read one at a time: three point one four. In a maths class the same number is three and fourteen hundredths.