Work out how many gallons of paint a room needs, accounting for coats, doors and windows so you buy once, not twice.
We measure the four walls, subtract the openings you won't paint, then multiply by the number of coats and divide by paint coverage.
One gallon covers roughly 350 sq ft on a smooth, primed wall. Rough, porous or dark-to-light surfaces cover less — add a coat if you're going from a dark colour to a light one.
A gallon covers about 350 square feet in one coat on a smooth, primed surface. Textured, porous or previously unpainted drywall can drop that to 250–300 sq ft, so round up.
Yes. We subtract about 21 sq ft per door and 15 sq ft per window. On a small room those openings are a meaningful share of the wall, so leaving them in over-orders paint.
Two coats is standard for a colour change or fresh drywall. Use one coat only for a light refresh of the same colour, and three when going dark-to-light or over a bold accent wall.
No — this figure is walls only. To paint the ceiling, add its area (length × width) and run it as a separate one- or two-coat job.
The Home Renovation Project Manager rolls every calculator into one budget — room by room, with a shopping list, contractor quote comparison and a live over-budget warning.