Lavender vs Calgar Blue

How close are they?

ΔE 21.9, loose: different enough that you should pick on purpose. Calgar Blue is a little darker, more saturated, cooler than Lavender.

Can I use Calgar Blue instead of Lavender?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Calgar Blue is a little darker, more saturated, cooler than Lavender.

Can I use Lavender instead of Calgar Blue?

The same difference applies the other way round: Lavender is a little lighter, more muted, 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.