How much exterior paint do I need?

Siding usually takes 250–400 sq ft per gallon per coat; rough stucco much less.

How do I measure a house?

Perimeter × wall height, plus gable triangles, minus doors and windows.

Two for color changes or bare surfaces.

Which exterior paint lasts longest?

Quality 100% acrylic: 8–12 years.

Elastomeric or regular paint?

Elastomeric bridges hairline cracks in stucco.

How much does it cost to paint a house?

Material, access and labor — get gallons here and build the quote.

Exterior paint calculator

House perimeter and height, openings, coverage, coats and can size: you get the paintable area, gallons and cans.

Purchase quantity

82.5 l

Net measurement: 75 l · Waste 10 %

Exterior paint6 bucket
Area to paint225 m²
Litres with waste82.5 l

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Calculate labour, margin & GST

How it's calculated (visible formula)

area = perimeter × height − openings; paint = area ÷ coverage × coats

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Measure perimeter and height of each wall (with gables).
Subtract doors and windows.
Check coverage for the surface (smooth or rough).
Work out gallons for two coats with waste.
Round up to 5-gallon buckets.

Worked example: House with 131 ft perimeter, 20 ft high, 160 sq ft openings

≈ 2,420 sq ft (225 m²)
÷ 250 sq ft/gal × 2 ≈ 19.8 gal (75 l)
+10% ≈ 21.8 gal

→ Five 5-gallon buckets.

Common mistakes

Using interior coverage on rough stucco.
Painting with rain or frost forecast.
Not treating cracks or mildew first.

Pro tips

Power-wash and treat mildew before painting.
Seal cracks with exterior elastomeric caulk.
Paint top-down in full sections to avoid lap marks.
Avoid painting walls in direct sun.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

Create quote Calculate margin & GST

FAQs

How much exterior paint do I need?: Siding usually takes 250–400 sq ft per gallon per coat; rough stucco much less.
How do I measure a house?: Perimeter × wall height, plus gable triangles, minus doors and windows.
One coat or two?: Two for color changes or bare surfaces.
Which exterior paint lasts longest?: Quality 100% acrylic: 8–12 years.
Elastomeric or regular paint?: Elastomeric bridges hairline cracks in stucco.
How much does it cost to paint a house?: Material, access and labor — get gallons here and build the quote.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.