HomeCal Pro - Calculation & Material Report
Tool: Paint Cost Calculator — Interior & Exterior Painting Estimator | Printed on:
Paint Cost Calculator — Interior & Exterior Painting Estimator
Estimate paint gallons, primer, supplies, and labor cost for interior and exterior painting.
Room Dimensions, Paint Tier & Coats
Wall Surface Area & Paint Coverage Formula
Transparent mathematical methodology explained in plain English.
Net Wall Area = (Perimeter × Wall Height) - (Doors × 21 Sq Ft) - (Windows × 15 Sq Ft) | Gallons = (Net Wall Area × Coats) / 350 Sq Ft per GallonCalculates total vertical wall area, deducts window and door openings, divides net area by 350 sq ft/gal standard coverage, and factors in primer, supplies, and painter labor.
Variables Explained:
- Room Dimensions (L × W × H): Room length, width, and ceiling height in feet.
- Number of Doors & Windows: Openings deducted from total wall square footage.
- Number of Coats: Recommended 2 coats for full color depth and durability.
- Paint Tier Price: Standard ($35/gal), Premium ($55/gal), or Designer ($80/gal).
15 ft × 20 ft Room with 9-Ft Ceilings (2 Doors, 3 Windows) — 2 Coats
Calculating paint gallons, ceiling paint, primer, and contractor labor.
- Total Gross Wall Area: (15 + 15 + 20 + 20) × 9 = 70 × 9 = 630 sq ft.
- Deduct Openings: 630 - (2 × 21) - (3 × 15) = 630 - 42 - 45 = 543 net sq ft.
- Calculate Paint Gallons (2 coats): (543 × 2) / 350 = 1,086 / 350 = 3.10 gallons -> Round to 4 Gallons.
- Ceiling Area (300 sq ft): 1 Gallon ceiling paint ($35).
- Materials Cost: (4 × $50) + $35 + $60 (tape, rollers, drop cloths) = $295.
- Professional Painter Labor (543 wall sq ft × $1.75/sq ft): $950.
- Total Project Cost: $295 + $950 = $1,245.
Frequently Asked Questions: Paint Cost Calculator
Click any question below to expand quick answers, formulas, and expert tips.
How much area does one gallon of paint cover?
One gallon of quality paint covers approximately 350 to 400 square feet of smooth wall space with one coat. Textured walls or porous drywall may reduce coverage to 250–300 sq ft per gallon.
Do I need primer before painting?
Primer is essential when painting bare drywall, covering water stains, painting over dark vibrant colors with a lighter shade, or transitioning from oil-based to latex paint. Many modern paints include paint-and-primer-in-one for standard repaints.