How many coats of paint do I really need?

Paint Calculator

Estimate how much paint you need for interior or exterior surfaces. Accounts for number of coats, doors, and windows.

Room Dimensions (Feet)

Length (ft)

Width (ft)

Ceiling Height (ft)

Doors

Windows

Coats of Paint

Coverage (sq ft/gal)

Paint Estimation Results

SPEC_VERIFIED

Total Paint Needed (Gallons)

2gal

Detailed Material Breakdown

Exact Paint Volume: 2.00gal
Paintable Area (Single Coat): 350 sq ft
Total Surface to Paint (2 Coats): 700 sq ft
Metric Equivalent: 7.6 liters

Calculation Formula & Assumptions

Estimates paint volume (gallons or liters) by calculating net wall area, multiplying by coat count, and dividing by the paint coverage rate.

Gallons = ⌈(Net Wall Area × Coats) ÷ Coverage Rate⌉

Step-by-step breakdown:

Sum the gross area of all walls: Total Wall Area = ∑(Width × Height)
Subtract door and window openings: Net Paintable Area = Gross Area − Openings Area
Multiply by desired coats (typically 2 coats): Total Paint Area = Net Area × Coats
Divide by paint coverage rate (typically 350 to 400 sq ft per gallon; 10 sq m per liter): Gallons = Total Area ÷ Coverage Rate
Round up to the nearest whole gallon or quart.

Note: Unprimed drywall, textured stucco, or dark-to-light color transitions absorb more paint; reduce coverage rate to 250–300 sq ft/gal.

Worked Calculation Example

Standard Bedroom (12×14 ft, 8 ft ceilings)

Painting two coats on four walls with 2 standard doors and 2 windows.

Room:12 ft × 14 ft, 8 ft high ceiling

Doors:2 doors (3×7 ft = 42 sq ft)

Windows:2 windows (3×4 ft = 24 sq ft)

Coats:2 coats

Coverage:350 sq ft/gal

Calculation Steps:

Perimeter = 2 × (12 + 14) = 52 ft
Gross Wall Area = 52 × 8 = 416 sq ft
Openings = 42 + 24 = 66 sq ft
Net Paintable Area = 416 − 66 = 350 sq ft
Two coats = 350 × 2 = 700 sq ft total paint area
Gallons = 700 ÷ 350 = exactly 2.0 gallons

Purchase 2 gallons of interior paint.

How to Use This Calculator

Enter room dimensions or individual wall dimensions.
Enter the number of doors and windows to subtract.
Select number of coats (2 coats recommended for almost all projects).
Select coverage rate (350 sq ft/gal is standard for quality interior paint).

Common Estimation Mistakes to Avoid

Applying only one coat and ending up with uneven sheen and patchy coverage.
Forgetting to budget separate ceiling paint (flat white).

Frequently Asked Questions

Two coats are almost always required for rich, uniform color depth and durability. One coat is only acceptable when touching up or refreshing the exact same color and brand.