Interior Walls

The "400 square feet per gallon" on the tin is measured on smooth, primed drywall. That is the best case, and it is rarely the case.

Spread rate belongs to the surface, not the paint. Primed drywall takes about 375 ft² per gallon. New unprimed drywall drinks 320. A textured wall takes 275. Wood siding takes 300. Stucco can halve the label figure to around 175.

Choosing paint by the coverage claim on the label compares products on a number that describes a wall you do not have.

The second coat is cheaper than the first

Once the surface is sealed, paint spreads about 15% further. Two coats is not twice one coat — it is about 1.87 times.

Doubling the first-coat figure is the most common over-buy in painting, and the surplus sits in the garage until it separates.

New drywall needs primer for a reason that is not adhesion

Paper and joint compound absorb at different rates. Paint straight onto unprimed board dries at different sheens over the joints and the field, and every taped seam shows through the finish in the right light. A drywall primer costs less than the extra finish coat it replaces.

Going over dark is a coats problem, not a coverage problem

The paint spreads normally. It just takes three coats — or two over a primer tinted toward the new color, which is almost always cheaper and faster.

Box the paint before you open a roller

Pour every tin into one bucket and stir. Tins of the same color from different batches differ slightly, and a wall painted from two of them shows the change exactly where you stopped for lunch.

Trim does not scale with the room

Doors, trim and ceilings are linear-foot work and a completely separate calculation. A room that takes three gallons of wall paint usually takes under a quart of trim enamel — and about three times as long to cut in.