Roof paint calculator
Roof coatings cover ~290 sq ft/gal on traditional roofs (asphalt, modified bitumen, concrete) and up to 500 sq ft/gal on smooth metal. Two coats are required — the first soaks in, the second forms the waterproof film. Best for low-slope and flat roofs.
The coverage math behind your estimate
The calculator takes your sloped roof area, applies your pitch factor, multiplies by the number of coats, and divides by the coverage rate for your substrate. Coverage is the lever that moves the number most, and it swings widely with the surface texture.
- Smooth metal: about 425 sq ft per gallon — the tightest, least thirsty surface.
- Corrugated or standing-seam metal: roughly 350 sq ft per gallon for the extra ribbed area.
- Asphalt and modified bitumen: around 290 sq ft per gallon; the granular surface drinks more.
- Concrete or clay tile: 200 to 250 sq ft per gallon, since porous tile soaks coating in fast.
Why two coats is non-negotiable
The first coat soaks into and seals the substrate; the second coat is what actually waterproofs and builds the dry film thickness the warranty depends on. Roof systems are rated at the full two-coat thickness — usually around 20 dry mils — so a single coat spends the gallons without earning the protection. The calculator defaults to two coats for exactly this reason, and offers three for severely weathered surfaces that bleed the first coat away.
Pitch factor and actual surface area
The sloped surface of a roof is always larger than the building footprint underneath it. A 1,500 sq ft footprint at a 4/12 pitch is roughly 1,725 sq ft of real roof to coat. Pick your slope in the pitch dropdown and the calculator multiplies the area up so you buy enough. Acrylic roof coatings belong on low-slope and flat roofs to seal seams and reflect heat; they are not a fix for steep shingle roofs or structural damage.
Prep and the weather window
Use a 3/4-inch nap roller on the first coat to force material into seams and texture, then an airless sprayer on the second coat for a uniform film. Do not spray the first coat on a textured roof — it bridges over voids instead of filling them. Plan a roughly four-day dry window: allow at least 24 hours between coats and keep rain out of the forecast for 48 hours after the final coat so the film can cure.
What it costs to coat a roof
Coating is priced by the square foot. Acrylic elastomeric material is about $0.75 to $2 a square foot, or roughly $15 to $30 a gallon, so a 1,500 sq ft low-slope roof is a few hundred dollars in material if you roll and spray it yourself. Power-washing the roof first adds about $0.20 to $0.60 a square foot, and a primer coat where the substrate needs it adds $1 to $2.
- Acrylic coating material: $0.75 to $2 per square foot.
- Pro-installed (prep, primer, two coats): $2 to $5 per square foot.
- Acrylic elastomeric, installed: $0.65 to $1.75 per square foot for the budget chemistry.
- Metal roof coating, installed: $1.50 to $3 per square foot.
DIY is mostly safe-access and labor, not material — the coating itself is cheap. Hiring a pro for a 1,500 sq ft roof typically runs $2,000 to $5,000 because two-coat application and roof prep eat the hours. For a paint-plus-labor estimate on any surface, use thepaint cost calculator.