How to Cite a Website in ACS Style

To cite a website in ACS style, give the author or organization, the title, the URL, and the date you accessed the page, in this pattern: Author or Organization. Title of Site. URL (accessed YYYY-MM-DD). The rule comes from the ACS Guide to Scholarly Communication (2020), the current authority for chemistry papers, and it splits into two templates depending on whether you are citing a whole site or one page on it. This guide shows both templates, eight worked examples that cover the web sources chemistry students actually cite (agency pages, LibreTexts-style open books, Wikipedia, PubChem, blogs, preprints), and the spots where an APA habit will quietly break an ACS reference.

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The official ACS rule for citing a website

The current authority is the ACS Guide to Scholarly Communication, published online in 2020. It replaced the ACS Style Guide, 3rd edition (2006), and its citation rules live in Chapter 4; the essential examples are free as the ACS Style Quick Guide (Section 4.3.3) on pubs.acs.org. Many library handouts still describe the 2006 edition, so if your handout disagrees with what follows, check which guide it was written from.

ACS gives two patterns for web content.

A whole website, or a page with no separate document title:

Author or Organization (if any). Title of Site. URL (accessed YYYY-MM-DD).

A specific document or page on a website, where the page has its own title and ideally a date:

Author 1; Author 2; Author 3. Title of Document. Title of Site or Organization, date. URL (accessed YYYY-MM-DD).

Four element rules do most of the work:

• Authors are inverted and separated by semicolons: Scalfani, V.; Guerra, J. ACS never uses an ampersand between names. For more than 10 authors, list the first 10, then et al.
• The main title is italicized. For a whole-site reference that is the site title; for a document reference it is the document title. This mirrors how ACS italicizes the journal name in an article reference: the italics mark the container-level or work-level title.
• The URL should be the stable public address of the page. The UC Berkeley library's ACS guide adds a warning worth repeating for anyone citing SciFinder or a paywalled database: do not paste session-specific URLs from subscription sites, because they die when your session does. Find the durable record link.
• The access date is written (accessed YYYY-MM-DD), so August 29, 2026 becomes (accessed 2026-08-29). University adaptations differ on whether every web reference needs one; the Quick Guide's own website examples carry it, and a page can change or vanish after you read it, so the defensible default is to include it on any source that lives only online. It records exactly which version of the page you saw.

If a page lists no publication date, write n.d. in the date position. Do not promote the site's footer copyright year into a publication date; it applies to the site, and rarely to the page.

For the journal-article, book, and patent formats that make up the rest of a chemistry reference list, see our complete ACS citation guide.

The three in-text systems, applied to websites

ACS lets a paper point to its references in three ways, and the website entry itself is identical in all three. Pick one system and hold it for the whole paper; mixing them is the error graders notice first.

1. Superscript numbers. The most common system and the one ACS journals themselves use. The number sits outside the punctuation: "...soil arsenic levels above the federal screening value.²"
2. Italic numbers in parentheses. The same numbering, set on the line: "...above the federal screening value (2)."
3. Author-date. "(CARO Analytical Services, n.d.)". ACS permits this system but its own journals do not currently use it, so reach for it only if your instructor asks.

Two consequences follow for web sources. In the numbered systems, references are numbered in order of first appearance, and a source keeps its number: if the EPA page is reference 2, it is still ² the fifth time you cite it. In the author-date system, a page with no personal author is cited by organization, and a page with neither author nor organization is cited by a shortened form of its title, with n.d. standing in for a missing year.

Worked examples

Each example shows the reference, then the in-text forms for a numbered paper and an author-date paper.

1. A page on a government agency site

U.S. Environmental Protection Agency. Toxics Release Inventory (TRI) Program. https://www.epa.gov/toxics-release-inventory-tri-program (accessed 2024-06-27).

In-text: ...reported under the TRI program.¹ / (U.S. Environmental Protection Agency, n.d.)

The agency is the author, spelled out in full. Government pages usually show no personal author and no publication date, which is why the access date matters here.

2. An organization's page with no personal author

CARO Analytical Services. Soil Testing Capabilities. https://www.caro.ca/soil-testings/ (accessed 2020-09-14).

In-text: ...commercial laboratories offer this panel.² / (CARO Analytical Services, n.d.)

This is the ACS Style Quick Guide's own website example. The company takes the author position and the page title is the italicized main title.

3. An authored page with a publication date

Scalfani, V. Computing InChIs. IUPAC FAIR Chemistry Cookbook, February 14, 2024. https://w3id.org/ifcc/IFCC012 (accessed 2025-03-03).

In-text: ...can be generated programmatically.³ / (Scalfani, 2024)

A page with its own author, title, and date uses the document pattern: the page title sits in roman, the site title is italicized, and the date follows the site title. This is the closest web citation gets to a journal-article reference, and it is the pattern to use for documentation pages and for chapters of open online textbooks like LibreTexts.

4. A whole website with several authors

Gálvez, M.; Guerra, J.; Crystal, F. Lonely Birder. http://lonelybirder.com/en/lonely-birder/ (accessed 2020-09-14).

In-text: ...as described on the authors' site.⁴ / (Gálvez et al., 2020)

Another Quick Guide example. Semicolons separate the inverted names, and the site title carries the italics because the reference is to the site as a whole.

5. A blog post

Stanchak, J. Best Chemistry Blogs: 5 Science Blogs Worth Bookmarking. ACS Axial, n.d. https://axial.acs.org/2016/07/18/must-read-blogs-for-chemists/ (accessed 2026-08-29).

In-text: ...several widely read chemistry blogs.⁵ / (Stanchak, n.d.)

A blog post follows the document pattern with the blog title italicized. This post shows no date on the page, so n.d. fills the date position even though the URL happens to contain one; cite what the page states, and let the access date do the version-tracking.

6. A Wikipedia entry

Chromatography. Wikipedia. https://en.wikipedia.org/wiki/Chromatography (accessed 2023-10-16).

In-text: ...a standard separation technique.⁶ / (Chromatography, n.d.)

No author is listed, so the entry title moves into the author position. The access date is doing real work here, because a Wikipedia article can change between your reading and your reader's. Whether Wikipedia is an acceptable source at all is a separate question your instructor decides; for a claim that matters, follow the entry's own footnotes to the primary literature and cite that instead.

7. A database record (PubChem)

Tin. PubChem, National Center for Biotechnology Information, n.d. https://pubchem.ncbi.nlm.nih.gov/element/Tin (accessed 2021-12-14).

In-text: ...melting point and isotopic abundances.⁷ / (Tin, n.d.)

Chemical databases are cited like websites: the record title (usually the substance name) leads, the database is the italicized container, and the hosting organization takes the publisher position. Use the record's stable URL, and include the CAS Registry Number in your text when it helps identify the substance precisely.

8. A preprint you found on the web

Sethuraman, S.; Westervelt, D.; Gong, K.; Grassian, V.; McNeil, V. F. Modeling and parameterization of size-dependent processes in multiphase aerosol chemistry, Ver. 2. ChemRxiv, April 20, 2026. https://chemrxiv.org/doi/full/10.26434/chemrxiv-2025-q36bp/v2

In-text: ...a size-dependent parameterization.⁸ / (Sethuraman et al., 2026)

A paper on ChemRxiv or arXiv is a preprint, and ACS has a dedicated pattern for it: authors, title, version number, italicized server name, posting date, then the DOI or URL. Reaching a source through a browser does not make it a website; cite what the thing is. The same logic sends a journal article you read online to the journal-article format, with the DOI.

Special cases

No author anywhere

Start the reference with the page title, as in the Wikipedia and PubChem examples. In an author-date paper the shortened title stands in for the surname; in a numbered paper nothing changes, because the number does the pointing.

No date anywhere

Write n.d. in the date position and keep the access date. Resist the temptation to mine a year out of the copyright line, a press-release date elsewhere on the site, or the URL.

The whole site versus one page

Citing a database or resource in general (PubChem as a tool, a society's website) takes the whole-site pattern with the site title italicized. Citing one page, record, or document takes the document pattern. If you quote or paraphrase specific content, cite the specific page, so your reader lands on the claim rather than on a homepage.

An online encyclopedia or handbook entry

Reference works that chemists reach through the browser, such as the CRC Handbook of Chemistry and Physics online or Ullmann's Encyclopedia, get a fuller pattern than an ordinary web page. The UC Berkeley library's adaptation of the guide gives the template:

Author, A.; Author, B. (if available) Article, Section or Table Title. In Encyclopedia or Handbook Title, edition; Publisher, posting date (if available). DOI or URL (accessed YYYY-MM-DD).

The entry or table title leads, the work's title is italicized with its edition number, and the publisher takes the position the host organization holds in a database reference. Entries in these works are often unsigned; when no entry author is given, start with the entry title, as with any authorless page.

Paywalled and session-based URLs

For SciFinder, Reaxys, and similar subscription tools, the URL in your address bar is often a session token that will not work for anyone else. Cite the stable record URL or DOI where one exists; where it does not, give the database's main URL and identify the record in your text by name and CAS Registry Number.

Your reference manager formats it differently

Zotero and Mendeley ship an ACS style based on the same guide, but webpage records with sparse metadata come out inconsistently: a missing "Website Title" field, for instance, silently drops the italicized container. Fill the record's fields in completely and check the output against the templates above rather than trusting it.

Common mistakes and how to avoid them

• Writing the authors APA-style. "Scalfani, V., & Guerra, J." is APA; ACS uses semicolons and no ampersand. This is the single most visible tell that a reference list was converted from another style by hand. If your course switches styles between classes, our APA website guide and MLA website guide show the same source types in those formats.
• Dropping the access date. Print sources never needed one, so it is the element students forget. For a page that can change, the access date is part of identifying the source.
• Writing the access date in prose form. The current guide's examples use (accessed 2024-06-27). A handout showing "(accessed June 27, 2024)" is following an older adaptation; either is understandable, but the YYYY-MM-DD form matches the 2020 guide and sorts cleanly.
• Italicizing the page title instead of the site title. In the document pattern the italics belong to the container: the site, the blog, the database. The page title stays roman.
• Giving a changed source a new number. In the numbered systems a source keeps its first number for the whole paper. Renumbering a repeat breaks every citation after it.
• Citing Google, or citing the search. The search engine is how you found the page; the page is the source. Cite the destination, with its own author, title, and URL.

Quick-reference table