Plurals of Acronyms and Abbreviations

Summary

To form the plural of an acronym or other abbreviation, simply add an s. No apostrophe is necessary.

Examples
  • ATMs, MBAs, PhDs, OTPs, URLs, PCs, DVDs, LANs, SSNs, VPs, ISBNs

To pluralize an abbreviation already ending in S, add another s or es.

Example
  • CMSs or CMSes

Don’t add s to form the plural of an abbreviated SI unit. These units do not have a separate plural form.

Example
  • 10 kg (not 10 kgs, for 10 kilograms)

Contracted professional titles such as Dr. and Prof. take an s at the end to form a plural, and the period denoting the abbreviation goes after.

Example
  • Drs. Who and Strange

The plurals of Mr., Mrs., and Ms. are Messrs., Mmes., and Mss. (or Mses.).

The general rule

Form the plural of an acronym or other abbreviation simply by adding an s at the end.

Examples
  • URL/URLs
  • WAN/WANs
  • DVD/DVDs
  • PC/PCs
  • HDD/HDDs
  • FAQ/FAQs
  • MD/MDs
  • EMT/EMTs
  • PhD/PhDs
  • MBA/MBAs
  • CEO/CEOs
  • VP/VPs
  • VIP/VIPs
  • ATM/ATMs
  • ISBN/ISBNs
  • MNC/MNCs
  • PSE/PSEs
  • REIT/REITs
  • NGO/NGOs
  • SSN/SSNs

An apostrophe before the s that forms the plural is not incorrect but generally omitted in formal writing.

Examples
  • URLs or URL’s
  • LANs or LAN’s
  • CEOs or CEO’s
  • PhDs or PhD’s
Tip

In formal writing, avoid using an apostrophe to create a plural form, unless not doing so would cause confusion.

Examples
  • Make sure to dot the i’s and cross the t’s before submitting your thesis.
    “Dot the is” would be confusing; the apostrophe improves clarity.
  • There are two a’s in abacus.
  • You must mind your p’s and q’s when dining with the Queen.

Plurals of abbreviations ending in S

An acronym or abbreviation that ends in an S sound can be pluralized either by adding s as usual or by adding es. Avoid inserting an apostrophe.

Examples
  • CMSs or CMSes
    both pronounced see-em-ess-es
  • SMSs or SMSes
  • DNSs or DNSes
  • PBXs or PBXes

Stay consistent in usage across a document.

Tip

Although the terms abbreviation and acronym are often used interchangeably, strictly speaking, only abbreviations pronounced as words are acronyms. Thus, while NATO and UNESCO are acronyms, USA and UN are initialisms.

Plurals of abbreviated units of measurement

Symbols for units of measurement do not have a separate plural form: don’t add an s to form the plural of an SI unit.

Examples
  • 5 kg (kilograms)
    read as five kilograms
  • 10 g (grams)
  • 10 cm (centimeters)
  • 50 ml (milliliters)
  • 10 s (seconds)
  • 100 m (meters)
  • 300 ms (milliseconds)

As you can see, not adding s to form the plural of an SI unit helps avoid ambiguity: otherwise, “100 ms” could be either 100 meters or 100 milliseconds.

Note that units of time (seconds, minutes, hours, months, and years) are often written with an added s to construct the plural form. This is considered acceptable in nontechnical, nonacademic writing. The period is optional.

Examples
  • 10 secs.
  • 60 mins.
  • 24 hrs.
  • 12 mos.
  • 300 yrs.

Plurals of abbreviated titles like Dr. and Mr.

To form the plural of a contracted social or professional title, simply add an s and move the period to the end.

Examples
  • Drs. Who and Strange are at the door.
  • We interviewed Drs. Keyland and Murphy.
  • Profs. Curie and Spivak are my idols.
  • Revs. Johnson and Obayi addressed the congregation.
  • We have spoken with Sens. Williams and Garcia.
  • Govs. Brown and Russo both refused to sign the bill into law.

The plural form of Mr. is Messrs. (an abbreviation of the French messieurs). It is now seen only in formal and legal writing.

Example
  • Messrs. Brown and Green signed the contract today at 2 p.m. EST.

The plural of Mrs. is Mmes. (for the French mesdames), now used in English only for humorous effect.

Example
  • Mmes. Brown and Green have arrived uninvited for tea, or perhaps to inspect our new furniture.

The title Ms. in the plural becomes Mss. or Mses.

Example
  • Mss. Roy and Desai write books for a living.
Note

In British usage, periods (or full stops) are omitted in contracted forms (e.g., Mrs Green, Mr Brown, Drs Jones and Smith).

Plurals of shortened forms

Shortened forms such as Vol. (for volume) and Ed. (for editor) take an s to form a plural. The period goes after.

Examples
  • Vols. 3–7
  • Robinson & Keating (Eds.)
Note

Convention dictates that in reference lists, the plural form of the abbreviation p. (page) is pp. (pages), not ps. Also, the abbreviation trans. (for translator) does not change in the plural.

Quick Quiz

Which is preferred in formal writing?
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Which is correct?
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Which is/are preferred?
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Did You Know?

Numerals shouldn’t be used at the start of a sentence.
Know more:How to Write Numbers: Numerals vs. Words