ACS Citation Format: A Complete Guide with Examples

ACS citation format is the referencing system used in chemistry, set by the American Chemical Society in the ACS Guide to Scholarly Communication (2020). A reference to a journal article looks like this: authors as surname plus initials separated by semicolons, article title, abbreviated journal name in italics, year in bold, volume in italics, issue in parentheses, page range, and DOI. In the text, you point to that reference with a superscript number, an italic number in parentheses, or an author-date pair. This guide shows the exact format for every common source type, the rules behind all three in-text systems, and the places where students most often lose marks.

To format an ACS reference automatically, use the AllCitations ACS generator. For the full list of supported styles, see the styles page.

The Official ACS Rule

The current authority is the ACS Guide to Scholarly Communication, published online in 2020. It replaced the ACS Style Guide, 3rd edition (2006), which is the version many older handouts and library printouts still describe. The citation rules live in Chapter 4 of the guide, and ACS publishes the essential examples free of charge as the ACS Style Quick Guide (Section 4.3.3) on pubs.acs.org.

Every ACS citation has two parts: a brief marker in the text and a full entry in the reference list at the end of the paper. The reference list entry for a journal article follows this pattern:

Format:

Author 1; Author 2; Author 3. Title of Article. Journal Abbreviation Year, Volume (Issue), Page Range. DOI

A real, checkable example:

Deno, N. C.; Richey, H. G.; Liu, J. S.; Lincoln, D. N.; Turner, J. O. Carbonium Ions. XIX. The Intense Conjugation in Cyclopropyl Carbonium Ions. J. Am. Chem. Soc. 1965, 87, 4533-4538. DOI: 10.1021/ja00948a024

Three typographic details carry the style: the journal abbreviation and the volume number are italic, the year is bold, and authors are separated by semicolons with each name inverted (surname first, then initials). Miss any one of these and the reference reads as almost-ACS, which a chemistry instructor will spot in seconds.

One change from the 2006 edition matters immediately: publisher location is no longer required for books. If a handout tells you to write "Oxford University Press: New York, 1998," it is teaching the old edition. Under the 2020 guide, "Oxford University Press, 1998" is complete.

The Three In-Text Citation Systems

ACS is unusual among citation styles in allowing three different in-text systems. Your instructor or target journal picks one; you use it consistently for the whole paper.

1. Superscript numbers. The reference number appears in superscript after the cited information: "Fluoride reduces enamel demineralization.¹" This is the system most ACS journals use and the one most courses mean when they say "cite in ACS."

2. Italic numbers in parentheses. The same number, but on the line in italics: "(1)". Some journals prefer this for manuscript submissions because superscripts are easy to lose in editing.

3. Author-date. The author surname and year in parentheses: "(Rakita, 2004)". The guide still documents this system, but ACS journals no longer use it in practice. You will mostly meet it in coursework where an instructor prefers name-based citations.

The numbered systems share a set of rules worth memorizing:

• Number sources in the order they first appear. The first source you cite is 1, the second is 2, and so on.
• A source keeps its number for the whole paper. Citing reference 3 again in the conclusion still produces a 3, never a new number.
• Cite several sources at one point by listing the numbers separated by commas, with a dash for three or more in a row: 1,5-7.
• Name authors in the sentence when it helps the prose. Two authors are joined with "and" (Jones and Smith¹³); for three or more, use the first author plus "et al." (Miller et al.⁵⁴).

Under the author-date system, in-text citations follow the same author rules: (Jones and Smith, 2019) for two authors, (Miller et al., 2021) for three or more.

These mechanics are common to numbered styles generally; if you have used IEEE or Vancouver, ACS will feel familiar. The differences sit in the reference list, and our guides to IEEE style and Vancouver style show the contrast. For a broader tour of how in-text citations work across styles, see the complete guide to in-text citations.

Ordering the Reference List

The order of the reference list depends on which in-text system you used:

• Numbered citations (superscript or italic): list references in numerical order, which is the order you first cited them. The list is deliberately not alphabetical.
• Author-date citations: list references alphabetically by the first author's surname.

Format the list with a hanging indent (first line flush left, subsequent lines indented) and start it on a new page under the heading "References." Sorting a numbered list alphabetically is one of the most common ways an otherwise correct paper goes wrong, because every in-text number then points at the wrong source.

Author Formatting Rules

ACS inverts every author name and reduces given names to initials:

• One author: Hammond, C.
• Two authors: Anastas, P. T.; Warner, J. C.
• Six authors: all six, semicolon-separated, in the order they appear on the paper.

The semicolon is the load-bearing character. ACS never uses an ampersand, and it does not switch to "and" before the final author the way APA does. Every author in the reference list gets the same treatment: Surname, Initial. Initial.; next author. The "et al." shortening belongs to in-text citations; the reference list in the guide's own examples names every author. If you are submitting to a specific journal that permits truncating very long author lists, follow that journal's instructions.

Journal Abbreviations Come from CASSI

ACS references abbreviate journal titles using the forms registered in CASSI (the CAS Source Index), which the Chemical Abstracts Service publishes as a free search tool at cassi.cas.org. Guessing abbreviations is the classic failure mode here, because some are not what intuition suggests.

Single-word titles such as Nature and Science are never abbreviated. When a journal is not in this table, look it up in CASSI before you submit; a wrong abbreviation is a wrong reference.

Worked Examples

Each example below shows the reference list entry and the superscript in-text form. Swap in an italic "(1)" or an author-date pair if your course uses those systems.

1. Journal Article with DOI

Deno, N. C.; Richey, H. G.; Liu, J. S.; Lincoln, D. N.; Turner, J. O. Carbonium Ions. XIX. The Intense Conjugation in Cyclopropyl Carbonium Ions. J. Am. Chem. Soc. 1965, 87, 4533-4538. DOI: 10.1021/ja00948a024

In-text: ...as shown for cyclopropyl carbonium ions.¹ Narrative form: Deno et al.¹ reported...

The 2020 guide recommends ending journal references with the DOI. Write it as shown or as a full https://doi.org/ link; either way, take it from the article's landing page and never guess one.

2. Journal Article with Issue Number

Tobisch, S.; Zühlke, D.; Bernhardt, J.; Stülke, J.; Hecker, M. Role of CcpA in Regulation of the Central Pathways of Carbon Catabolism in Bacillus subtilis. J. Bacteriol. 1999, 181 (22), 6996-7004.

In-text: ...regulates carbon catabolism.² Narrative form: Tobisch et al.² showed...

The issue number sits in parentheses, roman (not italic), directly after the italic volume. Include it whenever the journal supplies one.

3. Book

Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press, 1998.

In-text: The twelve principles of green chemistry³ define...

Book titles are italic, followed by a semicolon, then publisher and year. Add the edition after the title when there is one: The Basics of Crystallography and Diffraction, 4th ed.; Oxford University Press, 2015. No city, no state: that requirement ended with the 2006 edition.

4. Chapter in an Edited Book

Asmus, K. D. Recent Aspects of Thiyl and Perthiyl Free Radical Chemistry. In Active Oxygens, Lipid Peroxides, and Antioxidants; Yagi, K., Ed.; Japan Scientific Societies, 1993; pp 57-67.

In-text: Thiyl radical chemistry⁴ suggests...

The chapter author and chapter title come first, then "In" introduces the italic book title, the editor with the label "Ed." (or "Eds." for several), the publisher, year, and the chapter's page range with "pp".

5. Website

ACS Publications Division Home Page. https://pubs.acs.org (accessed 2026-08-05).

In-text: ...available from the publisher's site.⁵

Web references carry an accessed date in YYYY-MM-DD form because pages change. If the page has a personal author, start with the name in the usual inverted form; if not, start with the page title, as here.

6. Thesis or Dissertation

Enander, R. T. Lead Particulate and Methylene Chloride Risks in Automotive Refinishing. Ph.D. Thesis, Tufts University, Medford, MA, 2001.

In-text: A workplace exposure study⁶ measured...

Name the degree level exactly as the institution does (Ph.D. Thesis, M.S. Thesis). Theses keep their location because the institution, not a publisher, issues them.

7. Patent

Stern, M. K.; Cheng, B. K. M. Process for Preparing N-(p-nitroaryl)amides via Reaction of Nitrobenzene with Nitriles. US 5380946, 1995.

In-text: The patented process⁷ converts nitrobenzene...

Inventors are formatted like authors, followed by the patent title, the country code with patent number, and the year granted.

8. Reference Work or Standard Table

Chase, M. W., Jr. NIST-JANAF Thermochemical Tables, 4th ed.; American Institute of Physics, 1998.

In-text: Standard enthalpies were taken from the JANAF tables.⁸

Large reference works follow the book pattern. When you cite one specific table or entry, add the page or entry range after the year, the same way a chapter carries "pp".

Special Cases

No Author

Start the reference with the title. For a website, that is the page title followed by the URL and accessed date, as in example 5. In an author-date paper, the in-text citation uses a shortened title in place of the surname; in a numbered paper nothing changes, because the number does the pointing.

No Date

Web sources sometimes show no publication date at all. The accessed date in the reference covers you, since it records exactly when the content you cited existed. Do not invent a year from the site's footer copyright line.

Citing the Same Source Twice

Reuse the original number. If the fifth source in your paper comes up again three pages later, it is still ⁵. Numbering it again as a new source breaks the whole list, and this is the single most common structural error in student ACS papers.

Citing Software and AI Tools

The 2020 guide's quick guide section now includes guidance on citing generative AI, and it comes with a warning worth repeating: publishers and instructors differ on whether AI use belongs in the reference list, a disclosure statement, or nowhere. Check the policy that governs your paper before formatting anything. For conventional software, cite the developer as author, the software name and version, and the year.

Your Instructor Has Not Named a System

Ask if you can. If you cannot, use superscript numbers: it is the system ACS journals themselves use, so it is the defensible default. Whichever you choose, hold it for the entire paper. Mixed systems read as carelessness even when every individual citation is correct.

Common Mistakes and How to Avoid Them

• Following a 2006-era handout. The old 3rd edition required publisher locations and treated DOIs as optional. The 2020 guide dropped locations and expects DOIs for journal articles. Check the date on any ACS guide a course hands you.
• Alphabetizing a numbered list. Numbered references stay in citation order. Alphabetical order applies to author-date papers alone.
• Guessed journal abbreviations. "JACS" is a nickname, and Journal Am. Chem. Society is an invention. Look the title up in CASSI and copy the registered form.
• Flat formatting. The bold year and italic journal and volume are part of the style. A reference typed without them is incomplete even if every word is right.
• APA habits. Ampersands, "and" before the last author, and (Author, year, p. 5) page cites all belong to APA. ACS uses semicolons between all authors and no page numbers in-text. If you write in both styles regularly, our APA journal article guide shows the same sources formatted the APA way.
• Renumbering a repeated source. Assign each source one number at first citation and keep it.

Quick-Reference Table