1.04 Plurals

Add an s, but not an apostrophe, to form the plural of most abbreviations:

• ADMs
• BMWs
• CAs
• CRs
• FTEs
• GICs
• MPs
• PCBs
• 747s

Use an apostrophe and s to form the plural of numerical names of aircraft ending in a single letter:

• 727-100C’s
• 747B’s
• Cessna 402B’s

In cases where the resulting form would be ambiguous, add an apostrophe before the s:

• c.o.d.’s
• Q’s and A’s
• SIN’s

Add an apostrophe and s to form the plural of abbreviations containing more than one period, and an s without an apostrophe, to form the plural of abbreviations with only one period. In the latter case, the s precedes the period:

• G.M.’s
• Gens.
• pts.

The plurals of Mr. and Mrs. are irregular:

• Mr.
  • Messrs.
• Mrs.
  • Mmes.

The plural forms of the abbreviations for certain bibliographic references are different:

• l. (line)
  • ll. (lines)
• p. (page)
  • pp. (pages)
• f. (and the one following)
  • ff. (and those following)
• c., ch. (chapter)
  • c., ch. (chapters)
• MS (manuscript)
  • MSS (manuscripts)
• s. (section)
  • ss. (sections)
• subs. (subsection)
  • subss. (subsections)

Note that SI/metric symbols maintain the same form for both singular and plural and are written without periods, except at the end of a sentence:

• 1 cm
• 5 cm, centimetres
• 75 kg, kilograms
• The boxer weighed only 75 kg, kilograms.

7.64 Plurals

Certain plurals are sometimes written with ’s:

• abbreviations whose appearance would otherwise be ambiguous or confusing (see 1.04 Plurals) and the plurals of lower-case letters, symbols and numerals:
  • c.o.d.’s
  • x’s
  • +’s and -’s
  • POW’s
  • a’s and w’s
  • 6’s

  Another solution is to italicize the letter, symbol or numeral in question (see 6.11 Mathematical, statistical and scientific material).

• cited words:

  an overabundance of is’s and which’s

  It is not necessary to use the apostrophe in set expressions such as "the dos and don’ts," "no ifs, ands or buts," "the whys and wherefores."

• words not conveniently pluralized:
  • all the Toms, Dicks, Harrys and Louis’s
  • all the Lao’s in Laos

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