How much exterior paint do I need for a house?

For a house with exterior walls 36 ft × 24 ft and an 8 ft wall height, wall area = 2 × (36 + 24) × 8 = 960 sq ft. At 2 coats, that's 1,920 sq ft-coats — about 5.49 gallons at 350 sq ft/gal, rounded up to 6 gallons. Use the calculator above to subtract your actual windows and doors and add any gables separately.

Does this calculator include gable ends?

No. It measures the rectangular body of the house — perimeter × wall height — and gable ends (the triangular wall section under a peaked roof) aren't part of that formula. Estimate a gable's area separately (base × height ÷ 2) and add it to the total this calculator gives you.

Are trim and gutters included in this estimate?

No, not yet. Trim, fascia, and gutters are typically estimated separately from the wall body, often by linear foot or per piece rather than by area, since they use different coverage figures than a flat wall surface. This calculator covers the exterior wall body only.

How many coats does exterior paint need?

Two is standard practice for most exterior repaints, not a rule this calculator enforces — it's the default because a single coat rarely hides a color change evenly or holds up as well against weather over time. Set the coat count to what your specific project needs.

Do I need primer for exterior paint?

It's worth it for bare or new wood, unprimed siding, a major color change, or a surface with peeling or chalking paint. Primer seals raw material and improves adhesion in a way that matters more outdoors, where the finish has to survive weather. It's often skippable when you're repainting a similar color over a sound existing coat.

What's different between this and the interior paint calculator?

The underlying math is the same — wall area, coats, coverage range, gallon/quart rounding. The differences are in the guidance: exterior surfaces trend toward the low end of the coverage range more often, gable ends need a separate estimate this calculator doesn't compute, and trim/gutters aren't included on either calculator yet.

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Exterior Paint Calculator

Exterior paint is bought by area too, using the same wall-area math as interior paint, but real exterior surfaces rarely behave like the smooth, primed drywall the published coverage figures assume — siding texture, stucco, and years of sun and weather all change how far a gallon goes. This calculator uses the same dimensions-or-area entry and openings list as the interior paint calculator, applied to your house's exterior walls: enter your house's perimeter dimensions and wall height (or a wall area you already have), subtract windows and doors, set your number of coats, and toggle primer on if you need it. It covers the exterior wall body only — gable ends, trim, fascia, and gutters aren't part of this number; see the guidance below for what to do about each. The result rounds up to a whole gallon, or to quarts if a small job comes in under one.

Your room

LengthWidthCeiling heightUnit

Include ceiling

Doors & windows to subtract

CoatsTwo coats is standard practice for even color and durability, not a requirement — set this to what your project needs.Include primer (one coat)

Enter your room dimensions above to see results.

How it's calculated

The calculator finds gross wall area from your house's perimeter and height — 2 × (length + width) × wall height — or a direct area entry, then subtracts every window and door in your opening list. That net area is the rectangular body of the house, not including gable ends. It's multiplied by your number of coats to get the total area-coats to cover, then divided by a coverage rate in square feet per gallon; because coverage is a sourced range rather than one fixed number, the calculator shows both a single number to buy and the fuller range underneath it. Primer, if toggled on, is calculated separately and applied as a single coat regardless of how many coats of paint you're using. If the total for either paint or primer comes out under a gallon, the result switches to quarts.

Worked example

A single-story house with exterior walls 40 ft × 30 ft and a 9 ft wall height, with 8 windows (3'0" × 4'0") and 2 doors (3'0" × 6'8") subtracted: wall area = 2 × (40 + 30) × 9 = 1,260 sq ft. The 8 windows (8 × 12 = 96 sq ft) and 2 doors (2 × 20 = 40 sq ft) subtract 136 sq ft, leaving 1,124 sq ft net — the house body only; gable ends aren't part of this figure and need to be added separately if the house has them. At 2 coats, that's 1,124 × 2 = 2,248 sq ft-coats. At 350 sq ft per gallon, that's 2,248 ÷ 350 = 6.42 gallons — rounded up to 7 gallons, or 6–9 gallons across the full 250–400 sq ft/gal range. Real exterior jobs often land nearer the low end of that range (250 sq ft/gal) than the high end, since siding texture and sun-weathered surfaces soak up more paint than the smooth, primed surface the published figures assume.

Gables, openings, coverage, and trim

This calculator measures your house's exterior walls as a simple perimeter-times-height box: 2 × (length + width) × wall height, the same formula used for an interior room's walls. That captures the rectangular body of the house, but not gable ends — the triangular wall sections under a peaked roof, above the top of the straight walls. If your house has gables, estimate their triangular area separately (base × height ÷ 2 per gable) and add it to the total this calculator gives you; there's no field for it here yet. Windows and doors subtract the same way they do on the interior paint calculator: add each one to the opening list, from a preset or a custom size, and its area comes off the total automatically. Exterior surfaces trend toward the low end of the published coverage range (250 sq ft/gal) more often than interior walls do. Rough or textured siding, stucco, and brick all have more actual surface area per square foot of flat wall than smooth drywall; bare wood, unprimed siding, and previously unpainted trim soak up more paint before they're covered; and a sun-weathered, chalky, or previously peeling surface behaves more like a porous surface than a smooth painted one, even if it was smooth once. Budget toward the low-coverage end of the range rather than the display figure, especially for a first exterior coat. Trim, fascia, and gutters aren't part of this calculator yet — they're typically estimated separately, often by linear foot or per piece rather than by wall area, since they use different coverage figures than a flat wall surface. This page covers the exterior wall body only.

Where the coverage figures come from

Paint

BEHR's exterior painting guide — specifically about exterior work, and the primary citation for this page — states one gallon of any BEHR paint covers 250 to 400 square feet with one coat; porous, rough, textured, or previously unpainted surfaces need more, as does a dramatic color change. Sherwin-Williams states a gallon typically covers about 350 to 400 square feet. The two disagree on the low end, so the published range here (250–400 sq ft/gal) is the union of both rather than picking one. Exterior surfaces lean toward the low end of that range (250 sq ft/gal) more often than interior walls do: rough or textured siding, stucco, and brick all have more actual surface area per square foot of flat wall than smooth drywall, and bare, unprimed, or sun-weathered wood soaks up more paint before it's covered. We use 350 sq ft/gal as the display figure, drawn from:

Primer

Sherwin-Williams states a gallon of primer covers about 200 to 300 square feet. This figure is currently single-sourced — BEHR's published coverage guidance covers paint but not primer at the same level of detail — so it doesn't yet meet this site's usual two-source minimum. Treat it as a starting point and confirm with your primer's own label, especially for a large job. We use 250 sq ft/gal as the display figure, drawn from:

Sherwin-Williams — Paint Calculator

Common mistakes

Forgetting gable ends. The perimeter × height formula covers the rectangular body of the house, not the triangular wall section under a peaked roof — estimate gables separately and add them to the total.
Assuming exterior coverage matches interior. Rough siding, stucco, brick, and weathered or unprimed wood all use more paint per gallon than the smooth, primed surface published coverage figures assume — lean toward the low end of the range (250 sq ft/gal) rather than the display figure for a textured or first-time exterior coat.
Trying to fold trim and gutter paint into this total. They're usually estimated separately — by linear foot or per piece rather than by wall area — and aren't part of this calculator yet.
Skipping primer on bare wood, new siding, or a major color change. Exterior primer seals raw material and improves adhesion in a way that matters more outdoors, where the paint job has to survive weather rather than just look good.
Buying exactly to the calculated amount with no cushion. Exterior jobs are harder to touch up with a perfectly matched batch later — buying slightly over, especially near the low-coverage end of the range, avoids a mid-project supply run or a visible batch mismatch.

FAQ

How much exterior paint do I need for a house?: For a house with exterior walls 36 ft × 24 ft and an 8 ft wall height, wall area = 2 × (36 + 24) × 8 = 960 sq ft. At 2 coats, that's 1,920 sq ft-coats — about 5.49 gallons at 350 sq ft/gal, rounded up to 6 gallons. Use the calculator above to subtract your actual windows and doors and add any gables separately.
Does this calculator include gable ends?: No. It measures the rectangular body of the house — perimeter × wall height — and gable ends (the triangular wall section under a peaked roof) aren't part of that formula. Estimate a gable's area separately (base × height ÷ 2) and add it to the total this calculator gives you.
Why does exterior paint seem to cover less than the can says?: The can's figure is a best-case number for a smooth, primed surface. Rough or textured siding, stucco, and brick have more actual surface area per square foot of flat wall than smooth drywall, and bare, unprimed, or sun-weathered wood soaks up more paint before it's covered — all of which push real exterior jobs toward the low end of the published range.
Are trim and gutters included in this estimate?: No, not yet. Trim, fascia, and gutters are typically estimated separately from the wall body, often by linear foot or per piece rather than by area, since they use different coverage figures than a flat wall surface. This calculator covers the exterior wall body only.
How many coats does exterior paint need?: Two is standard practice for most exterior repaints, not a rule this calculator enforces — it's the default because a single coat rarely hides a color change evenly or holds up as well against weather over time. Set the coat count to what your specific project needs.
Do I need primer for exterior paint?: It's worth it for bare or new wood, unprimed siding, a major color change, or a surface with peeling or chalking paint. Primer seals raw material and improves adhesion in a way that matters more outdoors, where the finish has to survive weather. It's often skippable when you're repainting a similar color over a sound existing coat.
What's different between this and the interior paint calculator?: The underlying math is the same — wall area, coats, coverage range, gallon/quart rounding. The differences are in the guidance: exterior surfaces trend toward the low end of the coverage range more often, gable ends need a separate estimate this calculator doesn't compute, and trim/gutters aren't included on either calculator yet.