ΔE 12.2, fair: the same colour family, but not a straight swap. Saddle Brown is noticeably lighter, more muted than Chestnut Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Saddle Brown is noticeably lighter, more muted than Chestnut Brown.
The same difference applies the other way round: Chestnut Brown is noticeably darker, more saturated.
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 Chestnut Brown on the colour wheel See Saddle Brown on the colour wheel
All matches: Chestnut Brown equivalents · Saddle Brown equivalents