Exterior house paint calculator

Every line shows the quantity to buy and how StudSheet got it: the spacing, the waste and the package size, so you can check it before the supply house or the quote.

In Canada (12.19 m × 7.62 m house, 2 stories)

Set to Canada, the Sheet works the job out again for Ontario: metric sizes, bag sizes, the frost depth and the code notes. It doesn't just convert feet to meters. The first lines:

• 3 × 18.9 L + 1 × 946 mL, Exterior house paint: 211.3 m² of wood lap siding (217.4 m² of wall + 2 gables × 7.3 m² − 20.6 m² of windows and doors) × 2 coats ÷ 27.9 m² per 3.78 L = 57.4 L. 18.9 L pails cost less per litre than 3.78 L cans. Cans are counted at 3.78 L — read the litres on the can (Canadian “gallon” cans hold 3.6–3.79 L).
• 3 × 3.78 L, Exterior trim and door paint: 15.2 m² of window and door trim and corners + 21.1 m² of fascia and soffit + 2 doors (4.5 m²) = 40.8 m² × 2 coats ÷ 32.5 m² per 3.78 L = 9.5 L. One color for all of it — split it if the doors get their own.
• 1 × 3.78 L + 1 × 946 mL, Exterior primer (stain-blocking): 15% of 211.3 m² = 31.7 m² scraped to bare ÷ 27.9 m² per 3.78 L = 4.3 L. Stain-blocking, so cedar and redwood don’t bleed through (some say two coats on cedar).
• 1 × 946 mL, Exterior primer (stain-blocking): 15% of the trim = 5.4 m² ÷ 27.9 m² per 3.78 L = 0.7 L.
• 3 jugs (3.78 L), House wash concentrate: About one 3.78 L jug of concentrate per 92.9 m² (252.1 m²), mixed as the label says: dirt, chalk and mildew stop paint from sticking.
• 3 packs, Sandpaper, 80 and 120 grit: Feather the scraped edges so they don’t telegraph through: about a pack per 92.9 m² of wood — wet-sand by hand if there’s lead.

1. Lead check first: test the old paint (lab-tested chips, or a certified inspector) before any scraping or sanding.
2. Wash the house top-down with house wash and a garden hose — no pressure washer on old paint; rinse, then let it dry a day or two.
3. Scrape loose and peeling paint wet, by hand, over the plastic ground cover, feather the edges with sandpaper, and fill gouges and holes with exterior filler.
4. Spot-prime the bare spots, one coat.
5. Seal the gaps with exterior sealant: around windows and doors, along corner boards and trim joints — never the drip gaps under siding laps.
6. Cover plants and walks with drop cloths; take down lights, house numbers and shutters where you can.
7. Soffits and fascia first: they’re the highest, and drips land on unpainted siding.
8. Body: one side of the house at a time, top down, out of direct sun, brushing the laps and rolling the faces; finish whole boards or sections so the edges stay wet. Recoat once the first coat is dry to recoat — see the can.
9. Trim last: window and door trim, doors, brushed and mini-rolled, two coats.
10. Last coat: no rain or dew on it for at least 4 hours (the can says how long). Then pull tape, rehang what you took down, and label a can for touch-ups.

Must-have tools first, then the ones that help and the ones to rent for the day.

Mistakes that cost a callback or a second trip

• Painting over dirt, chalk or mildew: Paint peels off the dust, and mildew grows back through it. Wash, rinse and let it dry first.
• Painting in the sun or before dew: Paint flashes, laps and blisters in direct sun; late-day dew leaves streaks and surfactant drips. Follow the shade.
• Sealing the drip gaps: Caulking the bottom edges of lap siding traps water behind it. Seal joints at trim, not the laps.
• Dry-scraping or power-washing old paint: It spreads lead dust and chips into the soil where kids play. Test first, then work wet over plastic.

What the calculator assumes

• House: 40′ × 25′, 18′ from the ground to the eaves (about 9 ft a story).
• Coverage per gallon per coat: 300 sq ft on wood lap siding (rough and porous surfaces take more; labels range 250–400 on smooth siding), trim 350, primer 300.
• Openings: 15 sq ft a window, 21 sq ft a door, 63 sq ft or 112 sq ft a garage door. Trim: about 8 sq ft a window and 7 sq ft a door of casing; corner boards about 9″ of paint wide, top to bottom; fascia about 8″.
• Gables: half the width × the rise (6/12). Spot-priming covers 15% of the area on a scrape job; spraying uses about 25% more paint.
• Sealant: about 30 ft of ¼″ bead per 10.1 oz tube; half the joints need it.
• Ladders by Werner’s reach heights (24 ft reaches about 23 ft, 28 ft about 27 ft, 32 ft about 31 ft); higher than that, a lift or scaffolding.
• Lead: EPA’s RRP rule applies to paid work on pre-1978 homes, and to rentals. Outside, paid work that disturbs more than 20 sq ft of paint is covered.

The Sheet sets its code notes for the job's state or province. These are New Jersey's and Ontario's; the code reference has more. Always confirm with your building department.

• High walls: ladder work: The highest point is about 24 ft up, for a ladder of 28 ft — the riskiest part of the job. Set it 1 out for every 4 up on firm, level ground with a standoff, keep your belt buckle between the rails, and stay well clear of power lines. Many people hire out just the high walls and gables.
• Find out when the house was built: Homes built before 1978 may have lead paint, and outside paint often had the most. Test before you scrape or sand (a lab test of chips, or a certified inspector). If lead is present: mist and scrape by hand, no power sanding without a HEPA shroud, no open flame, no heat gun at 1,100°F or more, and no pressure washer; plastic on the ground 10 ft out from the wall, windows and doors closed within 20 ft, chips bagged every day, kids and pets away. EPA’s RRP rule doesn’t cover owners working on their own home, but anyone you pay must be an EPA lead-safe certified firm — for outside work that disturbs more than 20 sq ft of paint — and rentals are covered.
• Paint weather: Most exterior latex goes on from about 35–50°F up to 90°F, air and wall both, and needs those temperatures for at least 4 hours after (Behr’s exterior paints say 35–90°F; many paints need 50°F) — read the can. No rain or heavy dew on the way; paint the shady side and follow the sun around the house.

What materials do I need to paint the outside of a house?

For the worked example, a 40′ × 25′ house, 2 stories, the Sheet counts 14 lines with waste included, starting with exterior house paint (3 five-gallon buckets + 1 quart), exterior trim and door paint (3 gallons), exterior primer (stain-blocking) (1 gallon + 1 quart), exterior primer (stain-blocking) (1 quart). Each line's math is in the table above. Put in your own sizes in the exterior paint calculator and every line is counted again.

How long does it take to paint the outside of a house, and can I do it myself?

About 75 to 112 hours for the worked example, in 10 steps. StudSheet stamps it PRO STEP: dIY with a pro for one step.

What tools do I need to paint the outside of a house?

21 in all. The must-haves start with extension ladder (28 ft), ladder stabilizer (standoff), step ladder (6 ft), pump sprayer, carbide paint scraper, putty knife. On the Sheet you mark each one as owned, to buy or to rent.

Stuck while you paint the outside of a house? Ask in the Exterior painting group of the StudSheet community with this Sheet attached. Homeowners who've done it and verified pros answer, and anyone can read it.

• Painting for contractors: run this takeoff at your own prices, send the estimate, and get it signed and the deposit paid.
• Paint a room (14′ × 12′ room): Prep, primer, paint and supplies — walls, ceiling, trim and doors.
• Paint kitchen cabinets (20 doors, 8 drawers): Doors, drawer fronts and boxes counted into square feet: degreaser, sanding, bonding primer, cabinet enamel, rollers or a sprayer, and the days it takes.
• Stain or seal a deck or fence (16′ × 12′ deck): Cleaner, brightener or stripper, stain or sealer by the gallon for your deck, railings, stairs and fence — first and second coats counted the way the cans say.
• All 45 Sheets, across 16 trades.
• Code reference: frost depths, guard heights, stairs, retaining walls.