How many gallons of paint do I need for a 12x12 room?

A standard 12x12 foot room with 8-foot ceilings has roughly 384 sq ft of wall area. After subtracting one door and two windows, you have about 333 sq ft of paintable area. For 2 coats of paint, you will need approximately 1.9 to 2 gallons of paint.

How much wall area does 1 gallon of paint cover?

One standard gallon of interior or exterior wall paint covers between 350 and 400 square feet with a single coat on smooth, primed drywall.

How much area does a standard door and window take up?

A standard interior door subtracts approximately 21 square feet, and an average window subtracts roughly 15 square feet from your total wall square footage.

Paint Calculator — Estimate Gallons Needed for Walls & Rooms

Paint Coverage by Room Size Reference Chart

Room Type / Dimensions	Perimeter (ft)	Wall Area (8' Ceiling)	1 Coat Needed	2 Coats Needed
Small Bathroom (8 × 8 ft)	32 ft	~220 sq ft	1 Gallon	1–2 Gallons
Standard Bedroom (10 × 10 ft)	40 ft	~270 sq ft	1 Gallon	2 Gallons
Master Bedroom (12 × 15 ft)	54 ft	~380 sq ft	1 Gallon + 1 Qt	2–3 Gallons
Large Living Room (16 × 20 ft)	72 ft	~525 sq ft	2 Gallons	3 Gallons
Whole House (1,500 sq ft)	~250 ft interior walls	~2,000 sq ft	6 Gallons	11–12 Gallons

How to Calculate Paint Needed for a Room

A standard US gallon of interior wall paint covers approximately 350 to 400 square feet on smooth drywall. For rough surfaces or unprimed drywall, coverage may decrease to 300 square feet per gallon.

Standard Paint Calculation Formulas:

1. Total Wall Area = (Wall Length 1 + Wall Length 2 + Wall Length 3 + Wall Length 4) × Height

2. Openings Deduction = (Number of Doors × 21 sq ft) + (Number of Windows × 15 sq ft)

3. Net Paintable Area = Total Wall Area - Openings Deduction

4. Gallons Needed = (Net Paintable Area × Number of Coats) ÷ 350 sq ft per gallon

Step-by-Step Example Calculation

Suppose you are painting a 12 × 14 foot bedroom with 9-foot ceilings, containing 1 door and 2 windows, and you plan to apply 2 coats of paint:

Perimeter: 12 + 12 + 14 + 14 = 52 feet
Gross wall area: 52 ft × 9 ft = 468 sq ft
Deductions: 1 door (21 sq ft) + 2 windows (30 sq ft) = 51 sq ft
Net paintable area: 468 - 51 = 417 sq ft
Total coverage for 2 coats: 417 × 2 = 834 sq ft
Gallons: 834 ÷ 350 = 2.38 gallons → Round up and purchase 3 gallons (or 2 gallons plus 2 quarts).

Frequently Asked Questions

Should I always apply two coats of paint?

Yes. Even high-end paint-and-primer-in-one products look substantially more uniform, durable, and true-to-swatch with two even coats. One coat is generally only acceptable for minor touch-ups of the exact same color.

How much paint do I need for ceiling paint?

Ceiling area equals room length multiplied by room width (Length × Width). A 12x15 room has a 180 sq ft ceiling. One gallon of ceiling paint will cover up to 350 sq ft, easily handling 1 to 2 coats for an average room.

What is the difference between a quart and a gallon?

There are 4 quarts in 1 US gallon. If your calculation yields 1.2 gallons, buying 1 gallon plus 1 quart is often more economical than buying 2 full gallons.

Related Home Renovation Calculators

Flooring Calculator →Square footage, waste margin & box counts.Concrete Slab Calculator →Cubic yards and bags for patio slabs.Lumber Calculator →Board feet and framing material costs.