Paint Calculator
This paint calculator turns your wall dimensions, doors, and windows into the exact gallons of paint you need — doors (21 ft²) and windows (12 ft²) are deducted automatically, and results round up to the quarter gallon.
Your project
Your materials
Standard industry formulas with waste included. Always confirm quantities with your supplier.
How much paint do I need?
Multiply each wall's length by its height and add them up, then subtract 21 ft² per door and 12 ft² per window — the standard deductions painters use. A gallon of quality paint covers about 350 ft² per coat on smooth, primed walls; rough or porous surfaces cover less, so drop the coverage number. Two coats is the norm for a color change, and buying to the quarter gallon avoids paying for a full extra can.
Worked example. Take a 12 × 14 ft room with 8 ft ceilings, one door and two windows. The four walls total (12 + 14 + 12 + 14) × 8 = 416 ft². Subtract 21 ft² for the door and 24 ft² for two windows and you have 371 ft² of paintable wall. For two coats that's 371 × 2 = 742 ft² of coverage; at 350 ft² per gallon that's 2.12 gallons, which rounds up to 2.25 gallons — a 2-gallon purchase plus a quart.
| Paintable area | 1 coat | 2 coats | 3 coats |
|---|---|---|---|
| 200 ft² | 0.75 gal | 1.25 gal | 1.75 gal |
| 350 ft² | 1 gal | 2 gal | 3 gal |
| 500 ft² | 1.5 gal | 3 gal | 4.5 gal |
| 700 ft² | 2 gal | 4 gal | 6 gal |
| 1,000 ft² | 3 gal | 6 gal | 8.5 gal |
Assumes 350 ft² coverage per gallon, rounded up to the quarter gallon.