ΔE 19.3, loose: different enough that you should pick on purpose. Emperor Red is noticeably darker, more saturated, warmer than Moonpetal.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Emperor Red is noticeably darker, more saturated, warmer than Moonpetal.
The same difference applies the other way round: Moonpetal is noticeably lighter, 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 Moonpetal on the colour wheel See Emperor Red on the colour wheel
All matches: Moonpetal equivalents · Emperor Red equivalents