Calculator — Paint & Walls
Exterior Paint Calculator
Gallons of exterior paint from house footprint, wall height and gable ends — with siding coverage adjustment.
Inputs
Results
Adjust the inputs to see your result.
About this calculator
Exterior paint is estimated from paintable wall area, and the gable triangles are the part most estimates miss. This calculator adds both gable ends (half base times peak height each), deducts doors and windows, and adjusts coverage per gallon for smooth, textured or masonry surfaces.
What this number means
Exterior paint is estimated from the paintable wall area, and the part most estimates miss is the gable ends. A gable is a triangle: half the base times the peak height, counted once per end. On a typical two-storey gable house the triangles alone can add 10–15% to the wall area — skip them and you run short a gallon on painting day.
Coverage per gallon is not one number. Smooth siding takes the label figure of about 350 sq ft per gallon; rough-sawn wood and textured surfaces take closer to 300, and porous brick and masonry closer to 250. The calculator adjusts for the surface you pick, and the coat count multiplies the whole job — two coats means twice the coverage, not twice the gallons bought in a different size.
The formula
- Wall area = 2 × (Length + Width) × Wall height
- Gable area = 2 × (½ × Gable base × Gable peak height)
- Gross area = Wall area + Gable area
- Openings deducted = Doors × 21 sq ft + Windows × 15 sq ft
- Paintable area = Gross area − Openings
- Gallons = Paintable area × Coats ÷ coverage per gallon, rounded up
- Coverage per gallon: smooth siding 350, textured / rough-sawn wood 300, brick & masonry 250 sq ft
Worked example
A 40 × 30 ft house with 9 ft walls, 30 ft gable base and a 6 ft peak, 2 doors, 10 windows, 2 coats, smooth siding.
- Wall area: 2 × (40 + 30) × 9 = 1,260 sq ft
- Gable area: 2 × (½ × 30 × 6) = 180 sq ft
- Gross area: 1,260 + 180 = 1,440 sq ft
- Openings: 2 × 21 + 10 × 15 = 192 sq ft
- Paintable area: 1,440 − 192 = 1,248 sq ft
- Gallons: 1,248 × 2 ÷ 350 = 7.13 → 8 gallons
Assumptions and limitations
- One rectangular house footprint with two gable ends. For an L-shaped house, measure each block separately and add the paintable areas.
- Door deduction 21 sq ft (3 × 7 ft) and window deduction 15 sq ft (3 × 5 ft) are typical sizes — measure oversized openings separately.
- Enter gable base and peak as 0 for a hip roof, which has no gable triangles.
- Coverage figures are typical label values for exterior latex on each surface; a first coat over bare wood or masonry can run 10–20% lower — buy one extra gallon for a full repaint of unpainted siding.
- Trim, fascia and soffits are not included; estimate those separately by linear foot.
Frequently asked questions
A 2,000 sq ft house has roughly 1,600–1,900 sq ft of paintable wall area after gables and openings. At two coats on smooth siding (350 sq ft per gallon), that is about 10–11 gallons for the walls alone — run your exact footprint through the calculator rather than guessing from floor area.
Yes. Each gable end is a triangle — half the base times the peak height — and there are usually two of them. On a typical house they add 10–15% to the wall area, which is easily a full gallon on a two-coat job.
About 350 sq ft per coat on smooth siding, 300 on textured or rough-sawn wood, and 250 on porous brick and masonry. Bare, unprimed surfaces can run 10–20% lower on the first coat.
Yes — otherwise you overbuy. This calculator deducts 21 sq ft per exterior door and 15 sq ft per standard window. Measure picture windows and patio doors separately, since they are much larger than the standard sizes.
Two coats for a colour change or a full repaint — one coat over a matching colour in good condition can work, but the second coat is what gives uniform colour and full weather protection. Budget the job at two coats and treat one-coat coverage as a saving, not the plan.
Yes — a hip roof has no gable triangles, so enter 0 for the gable base and peak. The wall area alone is the gross area, which typically saves a gallon or two versus the same house with gables.