Exterior Paint Calculator
Gallons to paint a house exterior: wall area from the perimeter, height and gables, openings taken out, coverage by surface condition, plus primer.
Painting a house, counted from the sidewalk
An exterior is painted by its walls, so the area is the perimeter times the wall height — plus the gable triangles, the part tape measures forget from the ground: half the gable's width times its peak height, each. Doors and windows come back out. What the surface drinks decides the rest: a gallon covers about 350 sq ft on smooth, sound siding, 300 on an average repaint, and only about 200 on rough or thirsty work like stucco and bare wood — each figure per coat, and exteriors earn two.
Paintable area = perimeter × height + gables (½ × width × peak height) − openings · Paint = area × coats ÷ coverage · Primer = area ÷ primer coverage
Example: a 140 ft perimeter, 9 ft walls, two 30 ft gables peaking 8 ft up, and 200 sq ft of openings: 1,300 sq ft of paintable surface. Two coats at average coverage take 8 gal + 3 qt of paint, over 5 gal + 1 qt of primer.
Primer is its own line because it is not thinned paint: on bare wood, masonry, and stain-prone or chalky surfaces it is the coat that makes the paint stick and the color honest, at its own coverage (about 300 sq ft per gallon smooth, 250 average, 200 rough). Sound existing paint in a similar color can skip it — that is what the primer switch is for. Trim, fascia and doors are usually a second color and a second, smaller count; most painters price them by the opening and the linear foot rather than folding them into the wall gallons. And paint the weather, not the calendar: surfaces want to be dry, above about 50 °F, and out of direct midday sun, or the gallons you counted will not cure into the film you paid for. Painting inside a room instead? The interior paint calculator counts walls from the room's own dimensions.
Frequently asked questions
How much paint does a 2,000 sq ft house need?
House size in floor area is the wrong ruler — paint follows the perimeter and the height. A one-story 2,000 sq ft house (say 200 ft around, 9 ft walls, modest gables and openings) lands near 1,600 sq ft of paintable surface: about 11 gallons for two coats at average coverage, plus primer if the surface needs it. Run your own perimeter through the calculator; it is the number that counts.
One coat or two on an exterior?
Two, as the standard — the first coat seals and evens the surface, the second builds the film thickness that actually weathers. One-coat claims exist for premium paints over sound, same-color surfaces, but a color change, bare spots or a rough surface will show through one coat. Nobody regrets the second coat in year six.
Do I really need primer outside?
On bare wood, masonry, stucco and chalky or stained surfaces, yes — primer is the adhesion and stain-blocking layer, and paint skipped over it peels in sheets. Over sound existing paint in a similar color, a quality paint-and-primer product usually serves. Spot-prime every bare or patched spot either way.
Spray, roll or brush — does coverage change?
The can's coverage assumes the paint ends up on the wall. Spraying loses a share to overspray and wind (back-brushing or back-rolling a sprayed coat is standard practice for texture and adhesion); budget the rough-coverage figure if you will spray without back-rolling. Brushing and rolling tight, textured surfaces also drink more than the smooth number.
CalcCoverage