The Second Coat of Paint Uses Less Than the First

Coverage figures on a paint tin describe an ideal, sealed, smooth surface. The first coat on bare drywall, fresh filler, or chalky old emulsion is partly absorbed rather than deposited as film, so real coverage falls short of the label. Once that coat cures, the surface is sealed by the paint itself, and the second coat behaves much closer to the tin's number.

The practical consequence is that doubling your first-coat estimate over-buys. A better rule: full rate for coat one, roughly 80% of that for coat two. On heavily textured surfaces the gap narrows, because texture adds surface area to both coats equally.