Paint Calculator

Find Out How Many Gallons You Need

Room Details

Room Length (ft)

Room Width (ft)

Wall Height (ft)

Doors & Windows to Exclude (sq ft)

Number of Coats

Coverage (sq ft/gal)

Gallons to Buy

Enter your room details to see the estimate.

Validation Error

Enter valid room dimensions, coats, and coverage.

Understanding Paint Coverage

Buying too little paint means a mid-project store run with a possible color-batch mismatch; buying too much wastes money. This calculator estimates the gallons you need from your room's wall area, number of coats, and your paint's stated coverage.

Wall Area

Wall area = perimeter × height = 2 × (length + width) × height, minus the area of doors and windows.

Coats Multiply Area

Two coats need twice the paint of one -- most colors, especially reds and dark tones, need at least two coats for even coverage.

Check the Can's Coverage

Most interior paints cover 300–400 sq ft per gallon on a smooth wall -- check your specific product's label, since coverage varies by brand and texture.

Rounded Up to Whole Gallons

Since paint is sold by the gallon, the result rounds up -- buy a little extra for touch-ups and to match batch numbers.

Worked Example

Suppose a room is 12ft × 10ft with 8ft walls, 20 sq ft of doors/windows, 2 coats, and paint covering 350 sq ft/gallon:

Wall area: 2 × (12 + 10) × 8 = 352 sq ft.
Paintable area: 352 − 20 = 332 sq ft.
Total paint needed: 332 × 2 = 664 sq ft of coverage.
Gallons: 664 ÷ 350 ≈ 1.9 → buy 2 gallons.

Result

Paintable Area: 332 sq ft
Gallons to Buy: 2

Key Takeaways

Ceilings Are Separate: This calculator covers walls only -- add extra paint if you're also doing the ceiling.
Texture Reduces Coverage: Textured or porous walls (like new drywall) can need 20-30% more paint than the can's stated coverage.
Keep the Batch Number: Buy all your gallons from the same batch to avoid subtle color variation.