[Proposition 1.2.10(a)](https://books.google.com/books?id=LF6CbQk9uScC&pg=PA11) in "[Cohen–Macaulay Rings](https://doi.org/10.1017/CBO9780511608681)" by W. Bruns, H.J. Herzog: if $R$ is a Noetherian ring, $I$ an ideal of $R$, and $M$ a finite $R$-module, then
$$\operatorname{grade} (I,M)= \inf \{\operatorname{depth} M_p \mid p \in V(I)\}.$$