How does the term “about” affect claim interpretation?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The term “about” in patent claims requires careful consideration of context. According to MPEP 2173.05(b), “In determining the range encompassed by the term ‘about’, one must consider the context of the term as it is used in the specification and claims of the application.” The interpretation can vary based on the specific circumstances. For example, in W.L. Gore & Associates, Inc. v. Garlock, Inc., a limitation defining a stretch rate as “exceeding about 10% per second” was found definite because infringement could be clearly assessed. However, in Amgen, Inc. v. Chugai Pharmaceutical Co., claims reciting “at least about” were held invalid for indefiniteness when there was close prior art and no indication of the covered range.