How are numerical ranges in patent claims evaluated for definiteness?

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.

Generally, the recitation of specific numerical ranges in a claim does not raise an issue of whether a claim is definite. However, there are certain situations where numerical ranges can lead to indefiniteness:

• When a narrow range falls within a broader range in the same claim, it may render the claim indefinite if the boundaries are not discernible.
• Open-ended numerical ranges should be carefully analyzed for definiteness.
• The phrase “an effective amount” may or may not be indefinite, depending on whether one skilled in the art could determine specific values based on the disclosure.

As stated in MPEP 2173.05(c): “Use of a narrow numerical range that falls within a broader range in the same claim may render the claim indefinite when the boundaries of the claim are not discernible.”