A simple rule for using numbers in writing is that small numbers ranging from one to ten (or one to nine, depending on the style guide) should generally be spelled out. Larger numbers (i.e., above ten) are written as numerals.

When should numbers be written as words?

Numbers up to nine should always be written in words, anything higher than nine can be written in numerals. Alternatively, some guides suggest that if you can write the number in two words or fewer then use words rather than numerals.

Do you spell numbers under 10?

Numbers and ordered events less than 10 in full should be written as words, not numerals (see examples), although there are some exceptions. Numbers with two or more digits should be written as numerals unless they are at the start of a sentence (see examples).