2.10 Numerals and units of measurement

(a) Hyphenate compound cardinal and ordinal numerals from twenty-one (twenty-first) to ninety-nine (ninety-ninth) when written out:

  • There are twenty-nine members on the committee.

(b) Hyphenate a compound adjective in which one element is a cardinal or ordinal numeral and the other a noun:

  • a five-kilometre trek
  • a first-class coach
  • a $4-million project
  • a two-car family
  • a third-rate play
  • a 60-W bulb

Do not hyphenate before a symbol that is not a letter, and do not hyphenate a modifier in which the numeral, written in full, is itself a compound:

  • a 100 °C thermometer
  • a two hundred and fifty hectare farm

In cases such as the second example, use the abbreviated form (a 250-ha farm) if at all possible.

See 5.05 Adjectival expressions and juxtaposed numbers for further information.

(c) Do not hyphenate a possessive noun preceded by a numerical expression:

  • one week’s pay
  • 40 hours’ work
  • three weeks’ vacation
  • 10 months’ leave

(d) Hyphenate expressions of time of day as follows when writing out numerals:

  • eight-thirty
    • eight thirty-five
  • four-twenty
    • four twenty-six