How much paint do I need for a room?

For a 12×12 room with 8-foot ceilings (384 sq ft of wall), you need about 1 gallon for one coat or 2 gallons for two coats.

How many square feet does a gallon of paint cover?

One gallon of paint covers approximately 350-400 square feet per coat. Coverage varies by paint quality and surface texture.

Do I need one or two coats of paint?

Two coats are recommended for most projects—one coat rarely provides even coverage. New drywall or dramatic color changes may need 3 coats.

How do I calculate wall area for painting?

Multiply wall length by ceiling height. For a room: (Length × Height × 2) + (Width × Height × 2), then subtract doors and windows.

How much does paint cost?

Paint costs $20-$70 per gallon depending on quality. Premium paints cost more but provide better coverage, requiring fewer coats.

Should I subtract windows and doors from paint calculation?

Yes, subtract about 20 sq ft per door and 15 sq ft per window. Small areas like trim don't need subtraction.

Paint Calculator – Calculate How Much Paint You Need (2026)

What is a Paint Calculator?

A paint calculator is a home improvement tool that estimates how many gallons of paint you need for a room or surface. It calculates wall area, subtracts doors and windows, and applies paint coverage rates to determine the exact amount of paint required.

Buying the right amount of paint saves money and prevents waste. Too little paint means a mid-project trip to the store; too much means unused cans sitting in your garage. A paint calculator helps you buy the correct quantity the first time.

The calculator is useful for DIY homeowners, professional painters, and anyone planning a painting project. It provides accurate estimates for any room size, whether you're painting a small bathroom or a large living room.

How Much Paint Do I Need?

Determining how much paint you need involves measuring your walls and understanding paint coverage. Here's the process:

Measure Room Dimensions: Length, width, and ceiling height.
Calculate Wall Area: Perimeter × Height.
Subtract Openings: Doors (20 sq ft each) and windows (15 sq ft each).
Apply Coverage Rate: Divide by 350-400 sq ft per gallon.
Multiply by Coats: Account for 2-3 coats.

Paint Calculation Formula

Wall Area = 2 × (Length + Width) × Height

Deduction = (Doors × 20) + (Windows × 15)

Net Area = Wall Area − Deduction

Gallons = (Net Area × Coats) ÷ 350

Paint Cost = Gallons × Paint Price per Gallon

Example Calculation

12×12 room with 8-foot ceilings, 1 door, 2 windows, 2 coats:

Room Dimensions	12 ft × 12 ft
Ceiling Height	8 ft
Wall Area	384 sq ft
Door/Window Deduction	50 sq ft
Net Area	334 sq ft
Coats	2 coats
Total Coverage Needed	668 sq ft
Gallons Needed	1.9 gallons (buy 2)
Estimated Cost ($40/gal)	$80.00

Wall Area

Wall area is the total surface area you need to paint. Calculate it by multiplying the room perimeter (2 × length + 2 × width) by the ceiling height. For irregular rooms, calculate each wall separately and add them together.

Standard room dimensions and their wall areas:

10×10 Room (8 ft ceiling): 320 sq ft
12×12 Room (8 ft ceiling): 384 sq ft
12×15 Room (8 ft ceiling): 432 sq ft
15×20 Room (9 ft ceiling): 630 sq ft

Paint Coverage

Paint coverage refers to how many square feet a gallon of paint covers. Standard coverage is 350-400 square feet per gallon per coat. Premium paints may cover 400-450 square feet, while budget paints cover less.

Factors affecting coverage:

Paint Quality: Premium paints cover more.
Surface Texture: Rough surfaces absorb more paint.
Color Change: Dark-to-light or light-to-dark needs more paint.
Application Method: Sprayers use more than rollers.

Number of Coats

Most painting projects require two coats for even, professional-looking coverage. One coat is rarely sufficient, especially over new drywall, patched areas, or dramatic color changes.

When you might need three coats:

New Drywall: Prime and two coats minimum.
Dark to Light: May need primer + 2-3 coats.
Light to Dark: Two to three coats for even coverage.
Textured Walls: Additional coats needed.
Unpainted Plaster: Requires priming first.

Doors and Windows

Subtracting doors and windows from your calculation prevents overbuying paint. Standard deductions:

Standard Door: Subtract 20 sq ft
Standard Window: Subtract 15 sq ft
Large Sliding Door: Subtract 40 sq ft
Picture Window: Subtract 25 sq ft

Small openings like electrical outlets don't need subtraction. For rooms with many windows (like sunrooms), subtracting accurately can reduce paint needs by a full gallon or more.