When to spell out numbers vs use digits.
"Write five" or "write 5"? The answer depends on the number, the context, and which style guide you follow. Here are the rules that actually matter.
The common rule: small numbers as words
The most widely taught convention is to spell out small numbers and use figures for larger ones. The exact cutoff varies by style guide: many general-writing guides spell out numbers up to nine and use figures from 10 up; others (notably some journalism styles) spell out one through nine and use numerals for 10 and above. Pick one threshold and apply it consistently — inconsistency is more jarring to a reader than either choice.
Always use figures for these
Regardless of the small-number rule, figures are standard for measurements, money, percentages, dates, times, ages in tables, page and version numbers, and anything in a technical or data context. "Pay $3,250" is never "Pay three thousand two hundred fifty dollars" in running prose — though, crucially, finance documents often require both, which is the exception below.
Always spell out these
Spell out a number that begins a sentence ("Fifteen people attended", not "15 people attended"), or recast the sentence so it doesn't start with one. Spell out simple fractions in prose ("two-thirds") and casual or rounded quantities ("about a hundred").
The finance exception: both at once
Cheques, invoices, contracts and other financial instruments deliberately state an amount in both words and figures. This isn't redundancy — it's an error-check. If the figure is altered or misread, the words are the controlling record. That's why a cheque shows 3,250.00 in the box and "Three Thousand Two Hundred Fifty Dollars and 00/100" on the line. When you need that paired wording, the converter generates the words to match any figure.
Consistency beats the rule
Style guides disagree on the details, so the single most important thing is to apply one rule throughout a document. Mixing "5 apples" and "five oranges" in the same paragraph reads as carelessness, even though each is individually defensible.