Roof Coating Calculator
Work out how much elastomeric, silicone, asphalt or polyurethane roof coating to buy: litres or gallons for the coats you need, 19 L buckets, primer and reinforcing fabric for any roof area.
How it works
coating = area × coverage per coat × coats × (1 + waste) · buckets = ⌈coating ÷ 19 L⌉ (or 5 gal) · primer = area × 0.15 L/m² × (1 + waste) · 1 L/m² = 1 mm wet film ≈ 2.45 gal/100 ft²
Liquid-applied roof coatings are specified by coverage rate per coat, which is the same thing as wet film thickness: 0.6 L/m² lays down 0.6 mm (about 24 mils) of wet product. Acrylic elastomerics usually go on in two coats of 0.5–0.75 L/m² (1.25–1.8 gal/100 ft²); silicones in one or two heavier coats; asphalt and aluminum coatings at around 2 gal/100 ft². Rough or granulated surfaces absorb more, hence the waste allowance. A primer or diluted sealer helps adhesion on porous concrete, and polyester reinforcing fabric is embedded in the first coat over seams, cracks and drains — or over the whole roof for longer warranties. Always follow the product data sheet: the warranty depends on reaching its minimum thickness.
Worked example
An 80 m² concrete roof with two coats of acrylic elastomeric at 0.6 L/m² and 10% waste: 80 × 0.6 × 2 × 1.10 = 105.6 L — 6 buckets of 19 L. Primer 80 × 0.15 × 1.1 = 13.2 L, and reinforcing fabric for seams and cracks about 12 m².
Sources: Roof Coatings Manufacturers Association (RCMA) · ASTM D6083 — Liquid Applied Acrylic Coating Used in Roofing
Frequently asked questions
How many litres of roof coating per square metre?
For a typical two-coat acrylic system about 1.0–1.5 L/m² in total (0.5–0.75 per coat). Silicone needs about 0.8–1.0 L/m² per coat and asphalt or aluminum coatings 0.8 L/m².
How many gallons of elastomeric roof coating per 100 square feet?
Usually 1.5 gal per coat, so 3 gal per 100 ft² for two coats — enough for about 20–22 dry mils. Check the data sheet: 10-year systems often call for 2–2.5 gal per coat.
Do I need a primer?
On porous concrete, old asphalt and metal it improves adhesion and stops the coating from being absorbed; one coat at about 0.15 L/m² (or the diluted first coat many acrylic systems specify) is normal.
How long should I wait between coats?
Usually 4–24 hours depending on temperature and humidity, until the first coat is dry to the touch. Apply the second coat crosswise to the first and do not coat when rain or dew is expected.
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This calculator is for educational purposes. Double-check important results before acting on them.