Paint Calculator
Enter your room's dimensions, subtract the doors and windows, pick your coats — and get the gallons you actually need, plus a practical amount to buy at the store.
Paintable area
301
sq ft
Paint needed
1.72
gallons (6.5 L)
Buy
2 gallons
Deducts 21 sq ft per door and 15 sq ft per window. One gallon covers 300–400 sq ft on smooth, primed walls — use the low end for textured or porous surfaces, and budget two coats for any meaningful color change.
How Paint Coverage Works
Wall area is the room's perimeter times its ceiling height, minus openings — a standard door is about 21 sq ft and a window about 15 sq ft. A gallon of wall paint covers roughly 350 sq ft per coat on smooth, primed drywall. Two coats is the realistic default: one-coat coverage only holds up when the new color is close to the old one.
Formula
Wall area = 2 × (length + width) × height − openings Gallons = (wall area × coats) ÷ 350 Example: 12×10 room, 8 ft ceilings, 1 door, 2 windows: 2 × 22 × 8 = 352 − 21 − 30 = 301 sq ft 301 × 2 coats ÷ 350 = 1.72 gallons → buy 2 gallons
Frequently Asked Questions
How much paint do I need for a 12×12 room?
About 2 gallons for two coats on the walls: a 12×12 room with 8-foot ceilings has roughly 330 sq ft of wall after subtracting a door and two windows, and 330 × 2 coats ÷ 350 sq ft per gallon ≈ 1.9 gallons. Add about a gallon more to do the ceiling.
How many square feet does a gallon of paint cover?
300–400 sq ft per coat is the standard range, with 350 a safe planning number on smooth, primed drywall. Textured walls, bare drywall, and masonry drink more — figure the low end or below. A quart covers about 90 sq ft, enough for a door or accent wall.
Do I really need two coats of paint?
For any real color change, yes — one coat almost always shows roller marks and the old color underneath. One coat works when refreshing the same color or something very close. Dark or saturated colors over light walls can need a tinted primer plus two coats.
Do I need primer before painting?
Prime when covering bare drywall, patches, stains, glossy surfaces, or a dramatic color shift (especially over dark red or navy). For routine repaints in good condition, modern paint-and-primer-in-one products are genuinely sufficient.