ΔE 6.4, close: similar, with a visible difference side by side. USAF Brown is a little lighter, warmer than Ground Brown.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). USAF Brown is a little lighter, warmer than Ground Brown.
The same difference applies the other way round: Ground Brown is a little darker, 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 Ground Brown on the colour wheel See USAF Brown on the colour wheel
All matches: Ground Brown equivalents · USAF Brown equivalents