A Lesson From The Federal Circuit: "About” Or "Approximately” In Patent Claims May Render Them Indefinite And Invalid

Published: 2026-05-15 06:11:14 ET WOEN

Published on 05/15/2026 at 06:11 am EDT

Patent claims using general terms of approximation such as “about” or “approximately” may be at risk of invalidation when the terms are not well-defined. In a recent patent infringement case, Enviro Tech,1 the Federal Circuit affirmed a district court ruling that all asserted claims of U.S. Patent No. 10,912,321 were invalid as indefinite because the term “about” used in the claims did not have a clear meaning. The patent claims were directed to methods for treating poultry with peracetic acid to increase the weight of the poultry. In relevant part, the patent claimed processes for altering the pH of the treatment water to “a pH of about 7.6 to about 10.”

Why Did the Court Find “About” Indefinite in This Instance?

Under 35 U.S.C. § 112(b), a patent's claims must “particularly point out and distinctly claim the subject matter which the inventor or a joint inventor regards as the invention.” Under this statute, courts may hold that a claim is indefinite if it fails to inform, with reasonable certainty, those skilled in the art about the scope of the invention. The Federal Circuit reiterated that terms of degree like “about” and “approximately” are not inherently definite or indefinite under 35 U.S.C. § 112(b). Rather, they must be described with reasonably certainty, which depends on the particular technological facts of each case. Here, the court examined the claims, specification, and prosecution history and found that none provided the needed clarity, but rather when considered together created ambiguity as to the meaning of the term “about” as used in the patent claims. As a result, the claims were held to be invalid.

Key Takeaways for Patent Strategy

This decision does not prohibit the use of “about” or “approximately” in patent claims. It does, however, reinforce that patent holders should provide clarity when using such terms, else there may be an invalidation risk. If a patentee chooses to use words of approximation, a few practical steps to mitigate risk include:

Patent applicants and owners should exercise caution when drafting, prosecuting, or enforcing claims that rely on undefined terms of approximation, especially where those terms define boundaries that are critical to distinguishing over prior art. However, with careful attention to the definition of terms of approximation at the drafting stage as well as conscious awareness of these terms thereafter, risks can generally be mitigated.

Footnote

1. Enviro Tech Chemical Services, Inc. v. Safe Foods Corp, No. 2024-2160, slip op. (Fed. Cir. Dec. May 4, 2026). In the case, Enviro Tech sued Safe Foods alleging infringement of U.S. Patent No. 10,912,321. At the Eastern District of Arkansas, Safe Foods won its invalidity arguments on the basis of the term “about” in independent claim 1 as discussed herein, as well as on the basis that the term “an antimicrobial amount” also appearing in independent claim 1 was also indefinite. Because the CAFC affirmed invalidity on the basis of “about” being indefinite, it did not further address the alternative ground that “antimicrobial amount” was indefinite.

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