ΔE 9.0, close: similar, with a visible difference side by side. German Red Brown is a little lighter, more muted, cooler than Royal Brown.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). German Red Brown is a little lighter, more muted, cooler than Royal Brown.
The same difference applies the other way round: Royal Brown is a little darker, more saturated, warmer.
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 Royal Brown on the colour wheel See German Red Brown on the colour wheel
All matches: Royal Brown equivalents · German Red Brown equivalents