Cardinal Numbers
First decide what the number means: if it answers “how many?”, it is cardinal; if it identifies order, it is ordinal. Then apply the document’s number style. General house styles differ on when to spell out numbers, while measurements, dates, comparisons, tables, and scientific content often have special rules.
Cardinal numbers express quantity or count—“one,” “2,” “forty-five”—while ordinal numbers express position or sequence—“first,” “2nd,” “forty-fifth.” Whether a cardinal number should appear as a word or numeral is a separate style decision.
Key details
Further guidance
Identify
Ask whether the number gives a quantity (“three files”) or a position (“third file”). Quantity is cardinal; position is ordinal.
Presentation
After identifying the number type, follow the relevant house style for words versus numerals. Do not confuse that presentation choice with the cardinal/ordinal distinction itself.
Special Contexts
Expect numerals in many measurements, dates, comparisons, tables, mathematical relationships, and scientific contexts even when a general-prose rule would spell out small numbers.
Worked Example
“The team reviewed three proposals” uses the cardinal number “three”; “the third proposal” uses the ordinal “third.” A style guide may still require “3 proposals” in a particular technical context.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Cardinal number (opens in a new tab)Cambridge University Press · Defines cardinal numbers as numbers used to express amount, providing the terminology boundary against ordinal numbers.
- Choosing numerals or words — Style Manual (opens in a new tab)Australian Government Style Manual · General government-writing preference for readable large-number wording