Spell out whole numbers below 10 and use figures for 10 and above.
When the number is four digits or longer, separate with commas rather than spaces or periods.
For large numbers, it is better to use words or a combination of words and numbers.
Use figures in addresses (9 Elizabeth Avenue), in ages standing along after a name (Melanie, 3, has two brothers), in dates and years (AD 3, Dec. 8, 2003),
Spell out at the start of a sentence, if you must start with a number.
Do not spell out the year at the start, but avoid: 1972 was a leap year.
For the plural of numbers, including decades, do not use an apostrophe before the "s".
(For percentages, see the Spelling dictionary section.)