How Many Gallons of Paint Do I Need? Wall & Ceiling Estimates
Estimating paint requires finding the net surface area of your walls and ceilings. Having the right amount of paint ensures that you finish in one session and avoid shade mismatches caused by buying separate batches later.
Step 1: Calculate Gross Wall Area
- Room Perimeter = (Length × 2) + (Width × 2)
- Gross Wall Area = Perimeter × Ceiling Height
- Subtract openings: Net Area = Gross Wall Area - (Doors × 21 sq ft) - (Windows × 15 sq ft)
| Room Size (8ft ceiling) | Net Wall Area (2 doors, 2 windows) | Gallons Needed (1 Coat) | Gallons Needed (2 Coats) |
|---|---|---|---|
| 10 × 10 ft | 248 sq ft | 0.7 Gal | 1.4 Gal (buy 2) |
| 12 × 12 ft | 312 sq ft | 0.9 Gal | 1.8 Gal (buy 2) |
| 15 × 12 ft | 360 sq ft | 1.0 Gal | 2.0 Gal (buy 2) |
| 20 × 15 ft | 488 sq ft | 1.4 Gal | 2.8 Gal (buy 3) |
⚠️ Drywall primer warning: Drywall is highly porous and will drink paint. Always apply a coat of drywall primer sealer before painting unpainted board. Primers are much cheaper than topcoats and save you expensive gallons.
Frequently Asked Questions
How many square feet does a gallon of paint cover?
A standard gallon covers about 350 to 400 square feet of smooth, primed drywall. Highly textured or porous drywall may reduce this to 250 sq ft.
Do I subtract doors and windows from my wall area?
Yes. Deduct 21 square feet for each standard door and 15 square feet for each window to prevent over-purchasing paint.
Why does my room need two coats of paint?
Two coats provide uniform color saturation, mask underlying pigments, and offer a thicker, more durable finish that stands up to cleaning.