Numbers can be expressed in different forms depending on their purpose. Understanding cardinal and ordinal numbers helps you choose the right representation for your application.
Cardinal Numbers
Cardinal numbers express quantity—how many of something exists. "Three apples," "one hundred dollars," "two thousand users." These answer the question "how many?" Cardinal numbers are used in most numerical contexts: prices, quantities, measurements, and statistics.
Ordinal Numbers
Ordinal numbers express position or rank in a sequence. "Third place," "twenty-first century," "first customer." These answer "which one in order?" Ordinal numbers are used for rankings, dates, floor numbers, and sequential identifiers.
English Ordinal Rules
Most ordinals add "-th" (fourth, tenth, hundredth). Exceptions: first, second, third, and compounds ending in these (twenty-first, thirty-second). Numbers ending in 1, 2, 3 use -st, -nd, -rd unless the tens digit is 1 (eleventh, twelfth, thirteenth use -th).
Choosing the Right Form
Use cardinal for amounts and counts: "Pay five hundred dollars." Use ordinal for positions and dates: "Your fifth order" or "March twenty-third." Some contexts are conventional: "Chapter 5" vs "5th chapter" are both acceptable but one may be more common in your domain.