Paint Cost Estimator
Estimate how much paint you need and the total cost based on room dimensions, paint coverage rate, number of coats, and price per gallon.
Formula
Gross Wall Area = 2 × (Length + Width) × Height
Net Wall Area = Gross Wall Area − (Doors × 20 sq ft) − (Windows × 15 sq ft)
Total Area = Net Wall Area × Number of Coats
Gallons Needed = ⌈ Total Area ÷ Coverage Rate ⌉ (rounded up to whole gallons)
Total Cost = Gallons Needed × Price per Gallon
Assumptions & References
- Standard interior door area assumed to be 20 sq ft (approx. 3 ft × 6.67 ft).
- Standard window area assumed to be 15 sq ft (approx. 3 ft × 5 ft).
- Default paint coverage of 350 sq ft per gallon is typical for interior latex paint (range: 250–400 sq ft/gallon depending on brand and surface porosity).
- Gallons are always rounded up to avoid running short mid-project.
- Ceiling and trim are not included; add separate calculations for those surfaces.
- Two coats are recommended for most interior repaints; three or more may be needed for dramatic color changes or porous surfaces.
- Reference: Paint Quality Institute and major paint manufacturer guidelines (Sherwin-Williams, Benjamin Moore).