Last updated October 2026 · Reviewed by the CostWise Lab team
How much paint do I need?
Most interior paints cover about 350 square feet per gallon per coat on smooth, primed walls. A typical 14 × 12 ft bedroom with 8 ft walls has about 365 sq ft of paintable wall after subtracting one door and two windows. Two coats need about 2.1 gallons, so buy two gallons and a quart.
Quick guide by room size (walls only, 2 coats)
| Room | Wall area | Paint needed |
|---|---|---|
| Small bathroom (8 × 5 ft) | ~160 sq ft | ~1 gallon |
| Bedroom (12 × 12 ft) | ~330 sq ft | ~2 gallons |
| Living room (20 × 15 ft) | ~500 sq ft | ~3 gallons |
8 ft walls, one door and two windows, 350 sq ft per gallon.
Tips to avoid running out
- Buy all the paint at once so the color matches from can to can.
- Textured walls, fresh drywall and big color changes soak up more paint. Use a primer or plan an extra coat.
- Dark or bright colors often need a third coat for even coverage.
- Keep the leftover paint labeled with the room name for touch-ups.
Methodology
The calculator measures the four walls, subtracts standard openings and divides by the coverage per gallon.
ceiling area = length × width
gallons = area × coats ÷ coverage, rounded up to the nearest quart
A standard door is about 3 × 7 ft (21 sq ft) and a standard window about 3 × 5 ft (15 sq ft). The default coverage of 350 sq ft per gallon is typical of the range printed on most interior paint labels.
Sources
Frequently asked questions
How many square feet does a gallon of paint cover?
Usually 250 to 400 sq ft per coat, depending on the paint and the surface. Check the can label for the exact figure.
Do I need two coats of paint?
Usually yes. Two coats give even color and better durability, especially when changing colors.
How much paint for a 12 × 12 room?
With 8 ft walls, one door and two windows, about 330 sq ft of wall. Two coats need roughly 2 gallons.
Does primer count as a coat?
Primer improves adhesion and coverage but is not a finish coat. Calculate primer separately using its own coverage rate.