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

2.11 Fractions

Hyphenate fractions used as modifiers and written in full, unless the numerator or denominator already contains a hyphen:

• a one-third share
• twenty-fiftieths calcium

but

• one thirty-second
• twenty-nine fiftieths calcium (In this case numerals are preferable.)

Hyphenate fractions, Exception

one and a half months

Usage is divided on whether fractions used as nouns should be hyphenated. We recommend that the hyphen not be used in such cases:

• Four fifths of the load was wheat, and one fifth barley.

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