Paint Gallons

Exterior painting

Exterior paint calculator

Measure the house, choose the siding, get the gallons and buckets to buy.

  • Last checked: October 10, 2026
  • By the Paint Gallons editorial team

Estimate your exterior paint

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Units

Use feet, square feet and US gallons.

House

The long side of the footprint, corner to corner; assumes a rectangular house.

The short side, the one under the gable ends; also the base of each gable.

From the foundation to the eaves; for two stories, measure the full height.

Triangular wall ends under the roof; most gable roofs have 2. Enter 0 for a hip roof.

From the eaves line up to the roof peak; each gable = ½ × house width × this height.

Doors and windows

Each counted as 21 sq ft (3 × 7 ft); count a double garage door (about 112 sq ft) as 5 doors.

Each counted as 15 sq ft (3 × 5 ft).

Paint

Rough and porous surfaces take more paint: the can’s coverage is multiplied by 1 (smooth), 0.9 (wood lap), 0.8 (stucco), 0.7 (rough wood) or 0.6 (brick).

Two coats is the usual plan outdoors, and needed for a color change.

From the paint can label on a smooth surface; plan on about 350 sq ft per gallon if unsure.

Adds 10% for trim edges, touch-ups and roller or sprayer loss.

Your result will appear hereEnter your house’s length, width and wall height to see how much exterior paint you need.

Enter the house’s footprint and wall height, the gable ends under the roof, and how many doors and windows to leave out. The siding type adjusts the can’s coverage for rough or porous surfaces, and the result lists 5-gallon buckets, gallons and quarts.

  • Walls plus triangular gables
  • Five siding types, from vinyl to brick
  • Imperial or metric

How this is calculated

Wall area = 2 × (length + width) × wall height. Each gable adds ½ × house width × gable height. Doors (21 sq ft each) and windows (15 sq ft each) are subtracted. Paint = paintable area × coats ÷ (coverage × siding factor).

Example: a 40 × 30 ft house with 10 ft walls has 1,400 sq ft of wall. Two 6 ft gables add 2 × ½ × 30 × 6 = 180 sq ft. Two doors and ten windows take off 192 sq ft, leaving 1,388 sq ft. With smooth siding, 1,388 sq ft × 2 coats ÷ 350 sq ft per gallon = 7.9 gal: one 5-gallon bucket and three 1-gallon cans.

Written and checked by the Paint Gallons editorial team, against the sources below.

gallons = (walls + gables − doors − windows) × coats ÷ (coverage × siding factor)

Assumptions

  • Default coverage is 350 sq ft per gallon (8.5 m² per litre in metric), CompositePaint’s planning figure for exterior paint; exterior paint labels such as Glidden Fundamentals claim up to 400.
  • Siding factors come from CompositePaint’s coverage figures: vinyl, aluminum or smooth lap 1 (350–400 sq ft per gallon); wood lap, fiber cement or T1-11 0.9 (300–350); stucco 0.8 (it says add about 25%); rough-sawn wood, shingles or shakes 0.7 (about 250 against 350 for smooth cedar); brick or block 0.6 (as low as 200). Aluminum is treated as smooth siding; no source gave it a separate figure.
  • Doors count as 21 sq ft (3 × 7 ft) and windows as 15 sq ft (3 × 5 ft), the sizes CalculatorSoup uses; in metric, 2 m² and 1.4 m².
  • The house is a rectangle and each gable is a triangle over the house width. Trim, soffits, fascia and decks are not included.
  • The paint is rounded to one decimal place before cans are planned: 5-gallon buckets first, then 1-gallon cans, then quarts. Add 10% extra multiplies the paint by 1.1 before rounding.

Sources

Frequently asked questions

How much paint do I need for the outside of a house?

Add up the walls and gables, take off the doors and windows, multiply by the coats and divide by the coverage. A 40 × 30 ft house with 10 ft walls and two 6 ft gables needs about 7.9 gallons for two coats on smooth siding.

How do I measure a gable?

Measure the house width at the gable end and the height from the eaves line up to the roof peak. The gable is a triangle, so its area is half of width × height.

Does stucco or brick take more paint than siding?

Yes. Rough and porous surfaces soak up paint and have more surface for their size. The calculator multiplies the can’s coverage by 0.8 for stucco and 0.6 for brick or block, so the same wall needs more gallons.

Should I buy 5-gallon buckets?

For a whole house, usually yes: the calculator fills whole 5-gallon buckets first and then adds 1-gallon cans and quarts for the rest. Buying the color in buckets also keeps it consistent across the walls.

Does the estimate include trim and primer?

No. Trim, soffits, fascia and doors are usually painted in a separate color, and primer is a separate product. Use the paint cost calculator to add primer to your budget.

Painting inside as well?

The main paint calculator works out the walls of a room, with doors, windows and coats.

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