ΔE 11.8, fair: the same colour family, but not a straight swap. Grunge Brown is noticeably lighter than Middle Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Grunge Brown is noticeably lighter than Middle Brown.
The same difference applies the other way round: Middle Brown is noticeably darker.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Middle Brown on the colour wheel See Grunge Brown on the colour wheel
All matches: Middle Brown equivalents · Grunge Brown equivalents