ΔE 25.8, loose: different enough that you should pick on purpose. Copper is noticeably darker, more muted, warmer than Caesar Red.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Copper is noticeably darker, more muted, warmer than Caesar Red.
The same difference applies the other way round: Caesar Red is noticeably lighter, more saturated, 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 Caesar Red on the colour wheel See Copper on the colour wheel
All matches: Caesar Red equivalents · Copper equivalents