Inputs
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Enter your room details then click Calculate.
NAIBC / IRC codes
References & Sources
Standards Cited
- Manufacturer Guidelines — US Paint Manufacturer Coverage Specifications (Benjamin Moore, Sherwin-Williams, Behr)
Defines standard coverage rates for US-market paints, typically 350-400 sq ft per gallon for interior latex
Formulas Used
- Wall area:
wallArea = 2 x (roomLength + roomWidth) x wallHeight
Source: Basic geometry (room perimeter x height) - Net wall area:
netWallArea = wallArea - (numDoors x 21) - (numWindows x 15)
Source: Manufacturer guidance — Standard US door deduction: 21 sq ft (3ft x 7ft), standard window deduction: 15 sq ft - Effective coverage:
coveragePerGallon = baseCoverage x surfaceFactor
Source: Benjamin Moore / Sherwin-Williams guidelines — Surface factors: good condition 1.0, poor condition 0.8, new drywall 0.7 - Total gallons:
totalGallons = (totalArea / coveragePerGallon) x numberOfCoats
Source: Manufacturer guidelines - Cans needed:
cansNeeded = ceil(totalGallons)
Source: Standard US gallon can size
Key Assumptions
- Base coverage rates: interior latex 350-400 sq ft/gal (~12 m²/L), exterior 250-350 sq ft/gal (~8 m²/L), primer 300-350 sq ft/gal (~10 m²/L) — Benjamin Moore, Sherwin-Williams, Behr manufacturer specifications
- Surface condition factors: good (previously painted) 1.0, poor 0.8, new drywall/porous 0.7 — Manufacturer application guidelines
- Standard US door area deduction: 21 sq ft (3ft x 7ft) — Industry standard practice
- Standard US window area deduction: 15 sq ft (approx 3ft x 5ft) — Industry standard practice
- Standard US drywall sheet: 4ft x 8ft (32 sq ft) — Manufacturer standard sizes
- Standard can size: 1 US gallon (3.785 litres) — US paint manufacturer standard product sizes