🏠 Exterior Paint Calculator

How to Measure a House for Paint

Exterior paint estimating is one calculation with one trap in it. The calculation is simple; the trap is assuming the number printed on the can applies to your siding. It usually does not.

Measure the perimeter from the ground

Everything you need can be measured with both feet on the floor. Do not climb a ladder holding a tape measure.

• Perimeter. Walk each side of the house with a long tape or a measuring wheel and add the sides together. Include the sides of bump-outs, bays and attached garages. A rectangular 50 × 30 ft house has a 160 ft perimeter.
• Wall height — count the siding courses. This is the trick that removes the ladder entirely. Measure the exposure of one course of lap siding at eye level (commonly 4, 5, 6, 7 or 8 inches), count the courses from grade to soffit, and multiply. Twenty-seven courses at 4 in exposure is 108 in, or 9 ft.
• Expect about 9 ft of siding per 8 ft ceiling. The floor system and band joist add roughly a foot you would miss if you used the ceiling height. A two-story wall is usually 18 to 20 ft, not 16.
• Gable area = ½ × base width × rise. If you know the roof pitch, rise = (pitch ÷ 12) × (half the gable width). A 30 ft wide gable at 6/12 rises 7.5 ft, so it is about 112 sq ft. Hip roofs have no gables; a cross-gabled house can have four or more.
• Add 10% for a complicated house. Dormers, bays, jogs, a wrap-around porch and multiple rooflines all add surface that a perimeter measurement misses.

What to deduct, and what not to

• Deduct windows and doors. A standard window is about 15 sq ft and an exterior door about 21 sq ft. Garage doors are a big deduction and worth measuring: a 16 × 7 ft double is 112 sq ft.
• Do not deduct anything under about 10 sq ft. The extra cutting-in around a small basement window uses more paint than the opening saves.
• Soffit, fascia and porch ceilings are separate. They are usually a different color and often a different product. Count fascia in your trim linear feet and treat a large porch ceiling as its own area.
• Foundation walls are separate too. Exposed block or parged foundation takes masonry paint, not siding paint, and drinks it — see the spread rate table.

If you would rather measure wall by wall, our square footage calculator will add up irregular sections for you.

Spread Rate by Siding Type — the Number That Matters

This is the single most important section on this page. The 350 to 400 sq ft per gallon printed on a can of exterior acrylic assumes a smooth, primed, previously painted surface. Very few exteriors are that. Texture increases the real surface area and traps paint in every valley, and porous substrates absorb paint into themselves on the first coat.

These are typical one-coat spread rates. Ranges, not promises — coverage varies by product, film build and how heavily you apply, so always cross-check the figure on your own can and treat it as the optimistic end.

Put plainly: a textured surface commonly takes 30 to 50% more paint than smooth siding, and heavy stucco or bare cedar shakes can take close to twice as much. Running a house-sized estimate at the can rate when you have stucco is how people end up two or three gallons short with half a wall left and a color batch they can no longer match.

First coat vs second coat

On smooth siding the two coats use about the same amount. On rough or porous surfaces they do not: the first coat can use nearly twice what the second does, because it is filling texture and soaking into the substrate rather than building film. If your first coat empties more cans than you planned, that is normal on stucco, shakes and bare masonry — do not conclude you will need the same again for coat two.

Spraying changes the number too

Spraying uses 20 to 40% more paint than brushing and rolling, between overspray and the heavier film a sprayer lays down. If you plan to spray, add that on top of whatever the substrate already costs you.

When Exterior Paint Needs Primer

Primer on an exterior is not a formality — it is what stops the topcoat from peeling, and on some substrates it is the only thing that makes paint stick at all.

Prime, no argument

• Bare wood of any kind. Raw wood absorbs the binder out of finish paint. Use an exterior wood primer, and get it on within a couple of weeks of exposure.
• Cedar and redwood. These bleed tannins, which come through latex as brown or rust-colored streaks months later. You need a stain-blocking primer; a standard latex primer will not hold it back.
• Bare stucco, brick, block and concrete. Use a masonry primer, or block filler on CMU. Block filler covers only about 75 to 125 sq ft per gallon — a fraction of normal — because its job is to fill pinholes, not color anything.
• Chalky old paint. Rub a dark cloth on the siding. If it comes away powdery, wash the chalk off and use a bonding or masonry primer, or the new coat will simply peel off with the chalk layer.
• Every scraped or patched area. Spot-prime bare wood exposed by scraping. This is the common case, and it usually covers 10 to 25% of the wall.
• Bare metal, rusted nail heads and flashing. A rust-inhibiting primer, or you get rust bleed through the finish.

You can usually skip it

• Sound, clean, previously painted siding going into a similar color.
• Factory-primed fiber cement that is still clean and has not been exposed for months — but always prime freshly cut ends, which are raw.
• Vinyl siding in good condition, provided you use a paint rated for vinyl.

Two practical points. A tinted primer matched toward the topcoat frequently saves a whole finish coat on a big color change, and finish paint is more expensive than primer. And most exterior primers have a recoat window of 30 days or less — priming the whole house in April and topcoating in July means sanding and re-priming, so prime only what you can topcoat that season.

Temperature, Dew and the Weather Window

Exterior paint fails more often from being applied in the wrong conditions than from being the wrong paint. The label has a temperature range on it and it is not a suggestion — a coating applied outside its range never forms a proper film, and the failure shows up a season later as peeling or cracking that no amount of paint fixes.

• 50°F is the usual floor. Most exterior acrylics require air and surface temperature at or above 50°F. Some low-temperature formulations go down to 35 or 40°F; check the can, and buy that product deliberately if you are painting late in the season.
• The minimum applies for the whole drying period, not just while you are painting. This is the mistake. Painting at 60°F in the afternoon and dropping to 42°F at 2am ruins the film — latex coalesces as it dries, and a cold night stops that process permanently.
• Do not paint a hot surface in direct sun. Most products cap out around 90°F, and a south-facing wall in July can be 130°F. Paint skins over before you can keep a wet edge, and lap marks are guaranteed. Follow the sun around the house, painting the shaded side.
• Humidity below about 85%, ideally 40 to 70%. High humidity does not stop you painting, but it stretches the recoat time considerably.
• Stop before the dew point. Dew settling on a coating that has not dried causes surfactant leaching — brown, tan or clear streaks running down the finish. As a rule, stop painting two hours before sunset in autumn, earlier if the nights are cool. Clear autumn nights are the worst offenders.
• Rain. Most acrylics need 2 to 4 hours before light rain will not damage them, and some need 24. Check the can and check the forecast for the full window, not just the afternoon. A shower on green paint means washing the wall and repainting it.
• Wind. Above roughly 10 to 15 mph, spraying is not viable. Overspray travels much further than people expect, and cars, roofs and neighbors are all downwind of something.

In most of the US the best windows are late spring and early autumn. Midsummer is limited by hot sunlit walls; late autumn is limited by the nights, not the days, so check the overnight low before you open a can.

Sprayer vs Brush and Roll — and Why Back-Brushing Matters

Both work. They are not equivalent, and the right answer depends more on your siding than on your budget.

Back-brushing is not optional

A sprayer atomises paint and lays it on top of the surface. It does not push it into the grain of wood, into the pores of stucco, or behind the edges of a lap. Back-brushing — spraying a section and immediately following with a brush or roller before the paint sets — is what turns a sprayed coat into a bonded one.

On a previously painted, smooth, sound surface you can get away without it. On bare wood, rough-sawn siding, shakes, stucco and masonry, back-brushing the first coat is the difference between a job that lasts 10 years and one that peels in three. It also means spraying is realistically a two-person operation: one on the gun, one on the brush.

Practical setup

• Roller nap: 3/8 in for smooth siding, 1/2 in for wood lap and textured fiber cement, 3/4 in or more for stucco, brick and shakes.
• Brush: a 4 in flat for lap faces and a 2.5 in angled sash for edges and trim. Synthetic bristle for all waterborne exterior paint.
• Sprayer tip: a 0.015 to 0.019 in tip suits most exterior latex; larger for thick elastomerics on stucco.
• Work top down on each wall so drips land in wet paint, and keep a wet edge along the full length of a lap rather than stopping mid-run.

Prep Is Most of the Job

On an exterior repaint, 60 to 80% of the hours go into preparation, not painting. That ratio is the honest answer to why professional quotes look high, and it is the part DIY jobs most often shortcut. Paint applied over dirt, chalk, loose paint or bare rot fails, regardless of what it cost per gallon.

1. Wash

Every exterior needs cleaning first. Use a pressure washer at low pressure — 1,200 to 1,500 psi with a wide 25° or 40° fan tip, held 12 to 18 inches away, working downward with the laps. High pressure drives water up behind siding and into the wall cavity, and it will gouge softwood and blast out old caulk. On delicate or old siding, a garden-hose cleaner and a scrub brush is safer and not much slower.

Then let it dry. 24 to 48 hours for wood siding, and longer for masonry — stucco and brick can hold water for several days to a week after a heavy soaking, and painting over trapped moisture causes blistering.

2. Scrape and sand

Remove everything loose or flaking. Then feather the edges of the remaining paint with 80 to 100 grit so the transition does not telegraph through the new coat as a visible ridge. Spot-prime every bare area you exposed.

If the house was built before 1978, assume lead paint until a test says otherwise. Do not dry-sand, power-sand, or blast it with a pressure washer. Follow EPA RRP practices — wet methods, containment, and HEPA cleanup — or hire a certified contractor. This is the one item on this page that is a health issue rather than a finish issue.

3. Repair, then caulk

• Replace rotted boards before painting. Paint does not stop rot; it hides it while it spreads.
• Set popped nails and prime any bare metal so rust does not bleed through.
• Caulk after priming, not before. Caulk bonds far better to a primed surface than to bare wood, and primer over caulk can crack.
• Use an exterior-grade siliconised acrylic or polyurethane rated for 25 years or more. Cheap painter's caulk splits within a season or two outdoors.
• Caulk the right joints only: vertical butt joints, trim-to-siding, and around window and door casings. Do not caulk the bottom edges of lap siding or the horizontal joints the manufacturer tells you to leave open — walls need to drain and breathe, and sealing them traps moisture behind the cladding.

4. Protect

Cut back plants two to three feet from the wall and tie them off. Mask windows, light fixtures, meters and vents. Cover walkways, driveways and anything downwind if you are spraying. If you are working near the roof edge, check the roof area too — fascia, soffit and drip edge are usually painted at the same time and are easy to leave out of a materials list.

How Much Paint for a Typical House

Worked examples at two coats, with typical windows and doors deducted. The two right-hand columns are the same house in two different claddings, and the gap between them is the whole point of this page.

These round the net siding area to the nearest hundred square feet, so they can land a gallon either side of the calculator above for the same house. The calculator is the one to order from — it works from your actual measurements rather than a rounded typical.

Add on top of those figures:

• Trim and doors: roughly 1 gallon per 400 linear feet per coat, which is about 1 quart per 100 linear feet. A typical house has 250 to 500 linear feet of fascia, corner boards and casing.
• Primer: spot-priming a scraped house usually needs 1 to 3 gallons. Full priming needs about as much as one finish coat, and more on masonry.
• Soffit and porch ceilings: measure separately if they are a different color.

Buy the body color in one purchase and check the batch numbers match. If you need four gallons or more, price 5-gallon pails — they cost less per gallon and remove any risk of a visible difference between cans halfway along a wall. If you are buying separate gallons anyway, box them: pour them all into one bucket and mix before you start.

How long it should last

Sun exposure matters more than age. The south and west elevations routinely need attention years before the north side does, and repainting only those two walls is a perfectly legitimate way to spend half the money for most of the benefit.

Frequently Asked Questions

How much paint do I need to paint a 2,000 sq ft house?

Floor area is not the number that matters — siding area is. A 2,000 sq ft two-story house typically has around 2,300 sq ft of net siding, which is about 13 gallons for two coats on smooth siding and closer to 23 gallons on stucco. Add 1 to 2 gallons for trim and doors, plus primer if any surface is bare.

How much does a gallon of exterior paint cover?

On smooth, primed, previously painted siding, 350 to 400 square feet per coat. On textured surfaces it drops sharply: wood lap 275 to 325, T1-11 around 200 to 275, stucco 120 to 250 depending on the finish, and rough cedar shakes as low as 130. Coverage varies by product, so treat the can figure as the optimistic end.

Why does stucco need so much more paint than siding?

Two reasons. Texture means the real surface area is far larger than the flat measurement suggests, and paint fills every valley. And stucco is porous, so the first coat is partly absorbed into the substrate rather than forming a film on it. Expect a textured surface to take 30 to 50% more paint, and heavy dash stucco to take roughly double.

How do I measure the height of a two-story wall from the ground?

Count the siding courses. Measure the exposure of one course at eye level, count the courses from grade to soffit, and multiply. Twenty-seven courses at 4 in exposure is 9 ft. As a check, allow about 9 ft of siding per 8 ft ceiling — the floor system adds roughly a foot per story — so a typical two-story wall is 18 to 20 ft, not 16.

How do I calculate the area of a gable end?

A gable is a triangle: area = ½ × base width × rise. If you know the roof pitch, rise = (pitch ÷ 12) × half the gable width. A 30 ft wide gable at 6/12 pitch rises 7.5 ft, giving about 112 sq ft. A hip roof has no gables; a cross-gabled house can easily have four.

Should I subtract windows and doors from the siding area?

Yes for anything sizeable — about 15 sq ft per window, 21 sq ft per exterior door, and measure garage doors properly since a 16 × 7 double is 112 sq ft. But do not bother deducting anything under roughly 10 sq ft: the extra cutting-in around a small opening uses more paint than the opening saves.

Do I need to prime before painting the outside of a house?

Not everywhere, but definitely on bare wood, cedar and redwood, bare stucco or masonry, chalky old paint, bare metal, and every area you scraped back. Cedar and redwood need a stain-blocking primer specifically, or tannins bleed through as brown streaks. Sound, clean, previously painted siding going into a similar color does not need it.

What temperature can I paint outside?

Most exterior acrylics need air and surface temperature of at least 50°F, with some low-temperature products rated to 35 or 40°F. The critical point is that the minimum applies for the whole drying period, not just while you are painting — applying at 60°F and dropping to 42°F overnight ruins the film. Avoid surfaces above about 90°F or in direct hot sun.

How long does exterior paint need before it rains?

Most acrylics need 2 to 4 hours before light rain will not damage them, though some products specify 24 hours. Check your can and check the forecast for that whole window, not just the afternoon. Rain on paint that has not set means washing the wall down and repainting it.

What causes brown streaks running down fresh exterior paint?

Usually surfactant leaching — dew or rain landing on a coating that had not finished drying pulls water-soluble ingredients to the surface as brown, tan or clear runs. It is mostly cosmetic and often washes off, but the fix is prevention: stop painting about two hours before sunset, especially on clear autumn nights when the dew point is reached early.

Is it better to spray or brush and roll a house?

Spraying is 3 to 5 times faster and far better on shakes, stucco, spindles and lattice. Brushing and rolling uses less paint, needs almost no masking, and works the paint into the surface. The honest answer for most DIY jobs on smooth lap siding is brush and roll; spray only if the surface is genuinely rough or the house is large — and back-brush the first coat either way.

What is back-brushing and do I really have to do it?

Back-brushing means spraying a section and immediately following with a brush or roller before the paint sets, so it is worked into the surface rather than sitting on top of it. On sound, smooth, previously painted siding you can skip it. On bare wood, rough-sawn siding, shakes, stucco and masonry it is the difference between a coat that lasts a decade and one that peels in three years.

Does spraying use more paint than rolling?

Yes, typically 20 to 40% more, between overspray drift and the heavier film a sprayer lays down. If you plan to spray, add that on top of whatever your substrate already costs you. On a stucco house being sprayed, that stacking is how a 14-gallon estimate becomes an 18-gallon order.

Do I have to pressure wash before painting?

The house has to be clean; a pressure washer is just the fast way to do it. Use low pressure, 1,200 to 1,500 psi with a wide 25° or 40° tip held 12 to 18 inches away. High pressure drives water behind the siding and gouges softwood. Then let it dry — 24 to 48 hours for wood, and up to a week for soaked stucco or brick.

Can I paint vinyl siding?

Yes, but the color is restricted. Vinyl expands in sunlight, and a darker color than the original absorbs more heat and can warp or buckle the siding permanently. Use paint labelled vinyl-safe and stay at or above the original light reflectance value. Clean thoroughly first — vinyl chalks heavily — and paint on a mild, overcast day.

How many coats does exterior paint need?

Two is the standard and what almost every warranty assumes. One coat is only defensible as a refresh in the same color over sound paint. Go to three over bare wood, over new masonry, or for a big color change — though a tinted primer usually saves that third coat and costs less per gallon than finish paint.

How long does exterior paint last?

Typically 5 to 10 years on wood siding, 10 to 15 on fiber cement, 7 to 12 on stucco, and 4 to 8 on trim and doors, which always fail first. Sun exposure matters more than age — the south and west walls routinely need attention years before the north side, and repainting only those elevations is a legitimate way to spend half the money.