CategoriesPainting

Painting Calculators

Professional paint calculators to help you determine exact materials needed for walls, ceilings, and trim. Get accurate coverage estimates and cost projections.

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Paint is sold by the gallon and spread by coverage rate, and the surface decides the rate.

One gallon covers about 350 to 400 square feet on a smooth, previously painted wall. That figure drops fast on anything porous or textured: bare drywall, new plaster, rough render and popcorn ceilings can pull coverage down to 250 square feet or less. Multiply by the number of coats, and a room that looks like two gallons on paper becomes four in practice.

The other cost driver is what you are painting over. A dark colour under a light one, or bare wood and metal, needs primer first, and primer is its own coverage calculation. Skipping it usually means a third finish coat, which costs more than the primer would have.

Settle this before you calculate

Coats, not just area: Two coats is standard on a colour change. One is only realistic when refreshing the same colour on a sound surface.
Surface porosity: New drywall, bare wood and masonry drink paint. Assume 250 to 300 square feet per gallon rather than 400.
Trim and ceiling separately: They use different products at different rates. Rolling them into the wall figure is how people run short on the last window.

Where the estimate goes wrong

Subtracting every window and door: Leave small openings in the calculation. That extra area is roughly the waste in the roller tray, on the brush and left in the can.
Buying colour in separate batches: Tinted paint varies slightly between mixes. Buy all of one colour at once, and if you need more, take the can in for a batch match.
Painting over glossy or chalky surfaces: Glossy needs a scuff sand or a bonding primer; chalky needs sealing. Fresh paint on either will peel in sheets within a year.