Any sufficiently accurate lab meter is fine. The density is the logarithm of the ratio(posted 8855 days ago)time measured for unexposed film
over
time measured for area in question
Particularly when measuring high densities, make sure there is no stray light.
A second, though probably less accurate option might be using a gray step wedge printed at the same exposure as the negative in question. The density of the area in question is approximately that of the gray step having the same gray in the print.