Paint Calculator
Determine precise paint and primer gallon requirements with multi-wall dimensions, door/window deductions, surface porosity rates, and optimized container sizes.
Room Dimensions
Deductions (Doors & Windows)
Doors Specification
Windows Specification
Paint Specifications
Required Paint Volume
Estimated gallons, liters, and can packaging breakdown
3 Gallons
9.8 L
Recommended Purchase
3 × 1-Gallon Cans
Gross Wall Area 504.0 sq ft
Openings Deducted -72.0 sq ft
Net Surface / Coat 432.0 sq ft
Total Material Cost $126.00
Paint Coverage Formulas
Paint consumption is a function of net wall perimeter area minus architectural openings, multiplied by coat count and divided by manufacturer spreading rate per gallon.
Formula:
Gallons = [([2·(L+W)·H + Ceiling] - Deductions) × Coats] / Spreading_Rate (sqft/gal) Variables & Parameters
Wall Area 2 × (Room Length + Room Width) × Wall Height
Net Area Wall Area (+ Ceiling Area) - (Doors × 21 + Windows × 15)
Total Coated Area Net Area × Number of Coats
Gallons Required Total Coated Area / Surface Spreading Rate (sq ft/gal)
Frequently Asked Questions
How do you calculate paint?
To calculate paint quantity: (1) Measure wall perimeter and multiply by ceiling height to get total wall area (2 × [Length + Width] × Height). (2) Add ceiling area (Length × Width) if painting ceilings. (3) Subtract non-painted openings: 21 sq ft per standard interior door and 15 sq ft per standard window. (4) Multiply net square footage by number of coats (typically 2 coats). (5) Divide by paint spread rate (350 to 400 sq ft per gallon for smooth drywall) to find total gallons needed.
How much paint is for 1 sq ft?
On average, one standard US gallon (128 fl oz / 3.785 liters) of quality architectural paint covers approximately 350 to 400 square feet per coat on smooth drywall. This equals approximately 0.0025 to 0.0028 gallons (or 0.32 to 0.36 fluid ounces / 9.5 to 10.8 ml) of paint per 1 square foot of surface per coat. For a standard 2-coat paint application, budget approximately 0.0055 gallons (0.70 fl oz) per square foot.
How do you calculate paint for interior walls, exterior siding, and ceilings?
This paint calculator square feet tool functions as a complete paint calculator for walls, paint calculator interior, paint calculator exterior, and ceiling paint calculator. Multiply wall perimeter by ceiling height, add ceiling area if painting, and subtract doors (21 sq ft each) and windows (15 sq ft each). Divide by spread rate (350-400 sq ft/gal for smooth interior drywall, 250-300 sq ft/gal for textured exterior paint calculator surfaces) and multiply by coats.
How does this compare to a Sherwin Williams paint calculator or Behr estimator?
Like the sherwin williams paint calculator and other paint brand estimators, our tool calculates net square footage, 1-coat vs 2-coat requirements, and gives you an exact breakdown of 1-gallon and 5-gallon buckets to buy to minimize leftover waste.
How many square feet does 1 gallon of paint cover?
One US gallon of quality interior paint covers approximately 350 to 400 square feet on smooth, previously painted drywall. On rough, porous, or unprimed masonry surfaces, coverage drops to 200 to 250 square feet per gallon.