Summary
The plural and possessive forms of abbreviations follow a few simple rules—if you apply them consistently. SI units (kg, m, s) do not take an s in the plural (write “10 kg,” not “10 kgs”), while most other abbreviations pluralize with a bare s (“two NGOs,” “many DVDs”). Possession is formed with an apostrophe-s for singular (“the NGO’s mission”) and an apostrophe after a plural without changing spelling (“the NGOs’ missions”). Agreement matters: plural abbreviations take plural verbs.
Key points: choose one style (e.g., “hr/hrs” or just “h”), define each abbreviation on first use, pluralize without apostrophes (except certain single letters in some styles), and extend special formatting to the final apostrophe. Use discipline norms for dotted forms (Ph.D.s), doubled-letter plurals (p. → pp.; f. → ff.), and national variants (U.S./US). The tables and checklists below give copy-and-paste rules for theses and journal articles.
Bottom line: set a mini style sheet for your document and apply it relentlessly. Your abbreviations will be clear, correct, and publication-ready.
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The Plural and Possessive Forms of Abbreviations
Rules, edge cases, and a mini style sheet for theses and journal articles
Abbreviations are essential in academic and scientific writing: they save space, keep recurrent phrases readable, and match discipline conventions. But their plurals and possessives are fertile ground for small, highly visible errors that distract reviewers. Fortunately, a handful of rules covers almost every situation. This guide gives you those rules, then applies them to common families of abbreviations—SI units, acronyms, initialisms, dotted degrees (Ph.D.), and specialized scholarly shorthand (p./pp., f./ff.).
1) SI and other unit symbols: no plural s
In international scientific usage, unit symbols do not change in the plural: “1 kg,” “10 kg”; “3 m,” “25 m”; “5 h,” “12 h”; “45 min,” “30 s.” Never write kgs, ms (unless you mean milliseconds), or mins in formal science prose unless your journal explicitly permits it.
- Correct: 0.5 L, 3 L; 1 N, 20 N; 1 °C, 37 °C.
-
Incorrect: 3
Ltrs, 10kgs, 3ms(unless “milliseconds”).
Non-SI time abbreviations vary. Many journals accept yr/yrs and hr/hrs in prose; others prefer SI-style y and h (no s). Choose one convention and apply consistently (“hr/hrs” throughout, or “h” only).
2) Acronyms & initialisms: add a plain s for the plural
For most non-unit abbreviations, form the plural with a simple s, without an apostrophe:
- NGO → NGOs; DVD → DVDs; API → APIs; RBD → RBDs.
-
Verb agreement: “The NGOs are coordinating,” not “NGOs
is.”
3) Possessives: apostrophes mark ownership, not plurality
- Singular possessive: add ’s → “the NGO’s mission,” “the MRI’s resolution.”
- Plural possessive: plural + ’ → “the NGOs’ missions,” “the MRIs’ parameters.”
-
No apostrophe for plurals: “several NGOs,” not “
NGO’s.”
4) Dotted abbreviations & degrees: keep the dots, add the s
When an abbreviation includes periods (common in humanities or US styles), pluralize by adding s after the final period:
- Ph.D. → Ph.D.s (“two Ph.D.s contributed”).
- M.A. → M.A.s; B.Sc. → B.Sc.s (or degree names in full to avoid clutter).
Possessives follow the same pattern: Ph.D.’s dissertation (singular), Ph.D.s’ projects (plural). As always, your target journal’s style (with or without dots) prevails.
5) Doubled-letter plurals used in scholarship
Some long-standing editorial conventions pluralize by doubling the letter:
- p. (page) → pp. (pages): “see pp. 42–47.”
- l. (line) → ll. (lines) in some editions.
- f. (following page/leaf) → ff. (and following pages/leaves).
These forms are not possessive; they are specialized plurals used mainly in references or textual scholarship.
6) Articles with initialisms: a vs an
Choose an before an initialism pronounced with a vowel sound: “an MRI,” “an NGO,” “an SIR model”; use a before acronyms pronounced as words: “a NATO decision,” “a NASA engineer.” (This isn’t a plural/possessive rule, but it lives in the same sentences.)
7) Country abbreviations & style variants
National abbreviations vary by house style:
- US/UK (no periods) in many scientific journals; U.S./U.K. (with periods) in others.
- Possessives follow the same logic: “the US’s policy” or “the U.S.’s policy” (some guides prefer “the policy of the US/United States” to avoid clustered punctuation).
8) Single letters & symbols: apostrophes in some styles
Many style guides allow an apostrophe for clarity when pluralizing single letters or symbols: “Mind your p’s and q’s,” “two A’s and a B.” Others prefer no apostrophe (“ps and qs”). Pick one approach and be consistent; do not extend this exception to acronyms (“NGO’s” for plural remains wrong).
9) Capitalization, case, and typography matter
- Scientific units: distinguish look-alikes: MB (megabyte) vs Mb (megabit); m (metre) vs M (molar, mega-); s (second) vs S (siemens). Plurals do not change the symbol.
- Formatting possessives: if you bold or italicize an abbreviation in a heading, extend that formatting to the apostrophe: NGO’s, not NGO’s.
10) Big table of common patterns
| Type | Singular | Plural | Singular possessive | Plural possessive | Notes |
|---|---|---|---|---|---|
| SI unit | 1 kg | 10 kg | — | — | No plural s; symbol unchanged |
| Time (SI style) | 1 h | 6 h | — | — | Some journals allow hr/hrs—choose once |
| Acronym | NGO | NGOs | NGO’s | NGOs’ | Plain s; apostrophes only for possession |
| Initialism | MRI | MRIs | MRI’s | MRIs’ | “an MRI scan” (vowel sound) |
| Dotted degree | Ph.D. | Ph.D.s | Ph.D.’s | Ph.D.s’ | Keep dots per house style |
| Page ref. | p. 12 | pp. 12–15 | — | — | Doubled letters for plural |
| Following | f. | ff. | — | — | Meaning “and the following [pages/leaves]” |
| Single letter | A | A’s / As | A’s | A’s | Use apostrophe for clarity if permitted |
| Country | US / U.S. | — | US’s / U.S.’s | — | Often prefer “of the United States” in formal prose |
11) Agreement and syntax
-
Plural subject → plural verb: “RBDs were mapped,” not “
was.” - Abbreviation as adjective: keep the noun plural, not the abbreviation: “two DNA samples,” “several MRI scans.”
- Hyphenation: when an abbreviation modifies a noun, follow your style guide: “3D-printed scaffold,” “DNA-binding proteins.” The plural appears on the head noun (“proteins”), not the abbreviation.
12) Field-specific notes & edge cases
- Manuscripts: MS (singular) → MSS (plural) in some traditions; many modern journals prefer “MS”/“MSs.” State your choice once.
- Appendix labels: Fig. B2 is distinct from Fig. 2.2; pluralization does not change the internal numbering.
-
Latinisms: etc. has no plural form; do not write “
etc.’s.” Use possessives around the phrase instead: “the list’s etc. is unnecessary” → better: avoid entirely in formal prose.
13) Mini style sheet (copy/paste for your thesis)
Definition: Define every non-standard abbreviation at first mention: “non-governmental organization (NGO).” Re-define in each chapter if long gaps occur.
Units: SI symbols no plural s; space between number and symbol: “5 kg,” not “5kg.”
Plurals: acronyms/initialisms add s without apostrophe: “APIs, MRIs, NGOs.”
Possessives: ’s for singular (NGO’s); plural + ’ for plural (NGOs’).
Dotted degrees: Ph.D.s; singular possessive Ph.D.’s.
Pages/lines: p. → pp.; l. → ll.; f. → ff.
Articles: an MRI, an NGO; a NASA facility, a SARS-CoV-2 genome.
Consistency: choose hr/hrs or h; US or U.S.; stick to the choice throughout.
14) Common mistakes and quick fixes
| Mistake | Why it’s wrong | Fix |
|---|---|---|
| “10 kgs” | SI symbols don’t take plural s | “10 kg” |
| “The NGO’s are active” | Apostrophe used for plural | “The NGOs are active” |
| “Two PhD’s” (style with no dots) | Some journals prefer “PhDs” when dots are omitted | “PhDs” (or adopt dotted style consistently: “Ph.D.s”) |
| “MRIs’s resolution” | Double possessive mark | Singular: “MRI’s resolution”; plural: “MRIs’ resolution” |
| “pp 12–15” | Missing period after pp. | “pp. 12–15” |
15) Worked examples in context
Methods: Participants lay supine for 10 min. We recorded ECG signals with three MRIs; the MRI’s gradient strength was 45 mT/m (Site A).
Results: We analyzed data from three NGOs. The NGOs’ budgets increased by 12–18% year-on-year (5 yr window).
References: See pp. 214–219 and ff. for the full derivation.
16) Pre-submission checklist
- Every abbreviation is defined at first use and used consistently.
- SI units never take plural s; there is a space between number and symbol (except °, %, ‰ per house style).
- Acronyms/initialisms pluralized with plain s (no apostrophes).
- Possessives formed correctly for singular and plural (’s / ’).
- Dotted forms pluralized per house style (Ph.D.s / M.A.s) or undotted equivalents (PhDs / MAs) used consistently.
- Special scholarly plurals (pp., ff., ll.) used correctly in citations.
- Subject–verb agreement checked wherever an abbreviation is the subject.
- Formatting of final apostrophes matches the styled abbreviation in headings/figures.
Conclusion
Plural and possessive forms of abbreviations look small, but they carry large signals of care and credibility. Treat SI units as invariant symbols; add a bare s to pluralize most acronyms; reserve apostrophes for possession; and apply doubled-letter scholarly plurals where tradition requires. With a one-page style memo and the rules above, you can manage every abbreviation in your thesis or article cleanly and confidently.
