ΔE 13.3, fair: the same colour family, but not a straight swap. Steel Grey is a little lighter, more saturated, warmer than Medium Gray.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Steel Grey is a little lighter, more saturated, warmer than Medium Gray.
The same difference applies the other way round: Medium Gray is a little darker, more muted, cooler.
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 Medium Gray on the colour wheel See Steel Grey on the colour wheel
All matches: Medium Gray equivalents · Steel Grey equivalents