Exterior Paint Calculator
Exterior paint calculator for a whole house. Enter the footprint, stories, gables and siding type to get gallons of body paint, trim paint and primer to buy.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Total paint to buy
- 12 gallons
- Body, trim and primer are three different products, so buy them separately. 1,373 sq ft of body at 2 coats on smooth siding
- Body paint
- 8 gallons
- 1,373 sq ft at 2 coats, 350 sq ft per gallon. Buy 1 five gallon bucket plus 3 gallons: one batch, and cheaper per gallon
- Trim, soffit and fascia
- 2 gallons
- 350 sq ft of trim from 140 ft of eave and rake band plus casing around 14 openings
- Primer
- 2 gallons
- 343 sq ft primed at one coat. Bare wood, chalky paint and masonry all need it or the topcoat peels
- Surface measured
- 1,625 sq ft
- 1,400 sq ft of wall on 1 story at 10 ft per story, plus 225 sq ft in 2 gables, less 252 sq ft for openings
- Gable height
- 7.5 ft
- Peak above the wall plate at 6/12. This is the part that needs a ladder or staging, and it is easy to leave out of a measurement
- Paint when the surface is right
- 50 F and rising, dry 24 hours
- Most exterior latex needs a surface above 50 F, falling no lower overnight, and no rain for 24 hours. Painting in direct sun flashes the film and it will not level
- Planning estimate only
- Check the can for its spread rate
- Coverage on the label is for a smooth primed surface. Texture, porosity and a sprayer all move the real number
Exterior Paint formula
Wall area = Perimeter x Wall height per story x Stories
Gable area = Gables x 0.5 x Width x (Width / 2 x Rise / 12)
Body area = Wall area + Gable area - Openings x 18 sq ft
Body gallons = Body area x Coats / Spread rate for the siding, from 350 sq ft smooth to 160 on brick
Trim area = Perimeter x 1.5 ft of soffit and fascia + Openings x 10 sq ft of casingWorked example
A two story 50 x 28 ft house with rough sawn cedar lap siding, three gables on an 8 in 12 roof, 10 ft per story, 22 windows and doors, and a full prime because the old paint is chalking.
The perimeter is 156 ft, so the walls are 3,120 sq ft. Each gable is 9.3 ft tall and 131 sq ft, adding 392 sq ft. Openings take off 396 sq ft, leaving 3,116 sq ft of body. Rough sawn cedar covers only 250 sq ft per gallon, so two coats take 25 gallons, which is five 5 gallon buckets. Trim adds 3 gallons and the full prime adds 11. That is 39 gallons for a house whose walls would have taken 18 on smooth siding. The siding texture, not the size, is what drove it.
Quick reference
| Surface | Sq ft per gallon | Why |
|---|---|---|
| Vinyl or smooth lap | 350 | Factory smooth, takes the rated spread rate |
| Board and batten | 300 | Batten edges and vertical faces add surface |
| Rough sawn wood lap | 250 | Saw texture holds paint in the grain |
| Shake or shingle | 200 | Butt edges and course gaps, brush only |
| Stucco | 175 | Heavy texture, needs a spray and back roll |
| Brick or block | 160 | Porous masonry, and the first coat soaks in |
| Trim and fascia | 350 | Milled smooth, enamel spreads well |
| Primer on bare or chalky | 300 | One coat, before any of the above |
The siding surface matters more than the house size
Two houses with the same measured wall area can need twice the paint. A gallon covers about 350 square feet of smooth lap or vinyl siding, 250 on rough sawn cedar, 200 on shake, and as little as 160 on bare brick. That is the single biggest variable in the order, and it is the one the number on the can does not warn you about, because the label rate assumes a smooth primed surface.
Texture also changes the method. Smooth lap sprays and back rolls quickly. Shake has a butt edge and a gap behind every course that only a brush reaches, which is why a shake house takes longer as well as more paint. Stucco and masonry need a sprayer with a back roll to work the paint into the texture, and masonry needs its own primer first.
Measure the gables and respect the weather window
The walls are easy: perimeter times the height per story. The part people leave out is the triangle above the wall plate at each gable end. A gable over a 30 foot span on a 6 in 12 roof is 7.5 feet tall and 113 square feet, and a 10 in 12 makes it 188. On an L shaped house there may be three or four of them. It is also the siding that needs a ladder or staging, so it changes the labor as much as the paint.
Conditions decide whether the paint lasts. Most exterior latex wants a surface above 50 degrees that will not fall below it overnight, and 24 hours clear of rain. Painting a wall in direct sun is the common mistake: the film flashes before it can level, and the lap marks stay. Follow the shade around the house through the day rather than starting on the sunny side.
What this calculator leaves out
Everything before the first coat, which on an old house is most of the job: scraping, sanding, replacing rotten siding and trim, caulking joints, and washing off mildew and chalk. It does not price labor, staging or lift rental, and it does not size paint for a deck, a fence, a garage door, shutters or a metal roof, each of which takes a different product. Stain rather than paint on cedar or a deck follows different coverage entirely. Lead testing and the containment a pre 1978 house needs under the EPA rule sit outside it, as does any repair to the sheathing or housewrap found once the siding comes off.
Code limits that apply
- EPA 40 CFR 745.82
The lead rule applies to pre 1978 housing when exterior work disturbs over 20 sq ft of paint
If you miss it: A contractor working without certification faces federal penalties and the homeowner inherits contaminated soil
- EPA 40 CFR 745.85
No open flame burning, no torching, and no heat gun above 1,100 F on lead paint
If you miss it: Burning lead paint puts lead fume into the air around the house and into the attic
- EPA 40 CFR 745.85
Ground covering extends 10 ft from the structure, and power washing is not an allowed prep method
If you miss it: Chips and wash water carry lead across the yard, where it stays in the soil for decades
- EPA 40 CFR 745.84
The lead pamphlet goes to the owner and occupants before work starts, with a signed receipt
If you miss it: Missing pre renovation education is the most commonly cited violation of the rule
- EPA 40 CFR 745.89
The firm is EPA certified and a certified renovator is assigned to the job
If you miss it: An uncertified firm cannot legally do the work, and its insurer may decline a lead claim
Rows marked checked produce a warning in the results when an entry crosses the limit. The others are on the plans or on site and this calculator does not test them. Local amendments can be stricter; the adopted edition and the inspector govern.
Mistakes that cost money
- Measuring the walls and forgetting the gables. A steep gable over a wide span can be 150 sq ft of siding that only a ladder reaches.
- Using the spread rate on the can for rough siding. That number is for a smooth primed surface, and shake or stucco can take twice as much.
- Buying gallons one at a time. Batches differ slightly in color, and the difference shows across a wall in daylight.
- Painting in direct sun on a hot wall. The film flashes before it levels, leaving lap marks that no second coat hides.
- Skipping primer over chalky old paint. The new coat bonds to the chalk rather than the siding and sheets off within a season.
- Power washing a pre 1978 house to prep it. The EPA lead rule prohibits it as a prep method because it spreads lead paint chips across the yard.
Key facts
- A 40 by 30 ft one story house with smooth lap siding and two gables needs about 8 gallons of body paint for two coats, plus 2 of trim and 2 of primer.
- Exterior paint covers 350 sq ft per gallon on smooth lap siding but only 200 on shake and 160 on bare brick, so texture can more than double the order.
- A gable on a 6 in 12 roof over a 30 ft span is 7.5 ft tall and adds 113 sq ft of siding above the wall plate.
- Most exterior latex needs a surface above 50 F that will not drop below it overnight, and 24 hours without rain after application.
- The EPA Renovation, Repair and Painting rule applies to housing built before 1978 whenever exterior work disturbs more than 20 sq ft of paint.
- A 5 gallon bucket is cheaper per gallon than five separate gallons and removes the risk of a color shift between batches.
Frequently asked questions
How much paint do I need to paint the outside of my house?
A 40 by 30 ft one story house with smooth lap siding and two gables takes about 8 gallons of body paint for two coats, plus 2 gallons of trim and 2 of primer. Rough siding on the same house takes closer to 12 gallons of body.
How many square feet does a gallon of exterior paint cover?
About 350 sq ft on smooth lap or vinyl, 250 on rough sawn wood, 200 on shake and 160 on bare brick. The number on the can is the smooth primed rate, so texture is what moves your order.
Do I need to prime before painting the exterior?
Yes over bare wood, chalky old paint or any masonry. On a sound painted surface in the same color family you can skip it. Spot priming about a quarter of the house is the normal case on a repaint.
What temperature is too cold to paint outside?
Most exterior latex needs the surface above 50 F and not dropping below it overnight, though some formulas go to 35 F. Give it 24 hours clear of rain, and stay off walls in direct sun.
Sources and references
- Paint calculator and coverage per gallon (Sherwin-Williams)
- Paint calculator for walls, trim and doors (Benjamin Moore)
- Renovation, Repair and Painting Program, lead safe work practices (US EPA)
Next steps for this project
The usual order for a paint & walls project. See all paint & walls calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.