Join In
Twitter
YouTube
Weekly Newsletter
Libraries
A-Z Grammatical Terms
A-Z Confused Words
FAQs by Writers
A-Z Awkward Plurals
Punctuation Lessons
Common Mistakes
(ordered by seriousness) ESL Vocabulary Lists Parts of Speech Lists A-Z Idioms and Proverbs Tests and Games Top Tip Install a grammar checker
for your browser
(ordered by seriousness) ESL Vocabulary Lists Parts of Speech Lists A-Z Idioms and Proverbs Tests and Games Top Tip Install a grammar checker
for your browser
The Plurals of Abbreviations and Acronyms
The Quick Answer
The plural of an abbreviation is formed by adding "s." For example:- RTA > RTAs
- COS > COS's
- COS > COS'S
Forming Plurals of Abbreviations and Acronyms
The plural of an abbreviation or acronym is usually formed by adding "s" to the end. For example:- MOT > MOTs
- ATM > ATMs
- Once I have finished this PC, I will only have 3 PCs to configure.
- We have a dozen SUS's to collect from the station.
(In this example, the writer considers SUS's to be clearer than SUSs and has opted to use the 's version. This is acceptable. Be aware though that this could irk a fair proportion of your readers. Nevertheless, it is the writer's decision whether to use the apostrophe to aid understanding.)
- The firefighters could not assist with three of the RTAs because the BA's were still in the stores.
(There is no good reason to write BA's - especially after showing how abbreviations are pluralized with RTAs; i.e., it's also inconsistent.)

Pluralizing Abbreviations with Periods (
) / Full Stops (
)
The rule above applies to abbreviations with periods / full stops too. For example:
- Once I have finished this P.C., I will only have 3 P.C.s to configure.
- Not one of the S.O.S.'s was received by the coastguard.

This garage sign in the UK should say M.O.T.s not M.O.Ts.
- Anna was refused credit due to three C.C.J.s. and mortgage arrears.
- We have only done two M.O.T.s since January.
Avoid the Version with an Apostrophe
As covered in this lesson on apostrophes, "'s" can be used to show possession. For example:- The MP's photo shoot will be held at 7 o'clock.
In summary, you should be aware that the 's version is an option you can employ to assist the reader in spotting an unwieldy abbreviation instantly. However, in all other cases, you should opt for the "s" version.
Help Us Improve Grammar Monster
- Do you disagree with something on this page?
- Did you spot a typo?
Find Us Quicker!
- When using a search engine (e.g., Google, Bing), you will find Grammar Monster quicker if you add #gm to your search term.