I do this fairly regularly with my $20 Harbor Freight digital calipers. They are plenty accurate for this purpose and calipers can do both inside and outside measurements, unlike micrometers which are expensive and can only do one or the other. As mentioned above, measured both top to bottom and side to side due to possible distortion.

I used to do this kind of thing with vernier calipers, but the digital ones are way easier and very accurate. Since I bought mine I have found lots of other uses for them too.