How do I calculate wall square footage for painting?

Multiply 2 × (length + width) × ceiling height, then subtract about 20 sq ft per door and 15 sq ft per window. A 12 × 14 room with 8 ft ceilings, one door and two windows comes to 366 sq ft.

How much paint do I need for a 12 × 14 room?

About 2 gallons for two coats, at 350 to 400 sq ft per gallon.

How do I measure a house exterior for paint?

Multiply perimeter by wall height, then add each gable at width × height ÷ 2.

Why is my painter's square footage higher than mine?

Under PCA standard P10, small openings are not deducted and trim counts as 1 sq ft per linear foot.

All guides

How to measure square footage for painting

Interior wall area is 2 × (length + width) × ceiling height, minus about 20 sq ft per door and 15 sq ft per window. Exterior area is perimeter × wall height, plus each gable. Painters often measure differently, so expect their number to be higher than a DIY net figure.

Interior walls

Wall area = 2 × (length + width) × ceiling height. A 12 × 14 room with 8 ft ceilings has 2 × 26 × 8 = 416 sq ft of wall.

Subtract about 20 sq ft per door and 15 sq ft per window (Behr). With one door and two windows, that leaves 366 sq ft. Two coats at 350 to 400 sq ft per gallon is about 2 gallons.

Exterior walls

Exterior area = perimeter × wall height, plus each gable at width × height ÷ 2.

Example: a 30 × 40 two-story with 18 ft walls has a 140 ft perimeter, so 140 × 18 = 2,520 sq ft. Two 8 ft gables on the 30 ft ends add 2 × (30 × 8 ÷ 2) = 240 sq ft, for 2,760 sq ft gross and about 2,480 sq ft net after openings. At 250 to 300 sq ft per gallon, two coats take about 17 to 20 gallons.

Why a painter's number can be higher

Under PCA standard P10, small openings are not deducted.
Trim counts as 1 sq ft per linear foot.
Livable square feet is not the same as exterior paint area.

Use the Project Planner

The PaintersMN Project Planner asks for your home or project size and includes a wall-area helper, so painters start from a realistic scope.

Common questions

How do I calculate wall square footage for painting?: Multiply 2 × (length + width) × ceiling height, then subtract about 20 sq ft per door and 15 sq ft per window. A 12 × 14 room with 8 ft ceilings, one door and two windows comes to 366 sq ft.
How much paint do I need for a 12 × 14 room?: About 2 gallons for two coats, at 350 to 400 sq ft per gallon.
How do I measure a house exterior for paint?: Multiply perimeter by wall height, then add each gable at width × height ÷ 2.
Why is my painter's square footage higher than mine?: Under PCA standard P10, small openings are not deducted and trim counts as 1 sq ft per linear foot.

Sources

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