Professional Interior Painting Cost Calculator
Estimation Summary
How to Estimate Interior Painting Costs
Planning a home renovation requires precise budgeting, and painting is often the most cost-effective way to transform a space. To accurately calculate the cost of painting a room, you must consider the total surface area, the quality of materials, and whether you intend to hire a professional or tackle the project yourself.
1. Calculating Surface Area
The first step is determining the square footage of the walls. Use the formula: 2 × (Length + Width) × Height. However, you shouldn't pay for paint you won't use. Subtract approximately 21 square feet for every standard door and 15 square feet for every average-sized window. This gives you the net paintable surface area.
2. Paint Coverage and Quantity
A standard gallon of paint typically covers between 350 and 400 square feet with a single coat. For a professional finish, two coats are almost always required. If you are painting over a dark color with a lighter one, you may even need a third coat or a dedicated primer layer.
3. Material vs. Labor Costs
Material costs are relatively predictable. Economy paints start around $25 per gallon, while designer or "scuff-proof" premium paints can exceed $75 per gallon. Labor is the largest variable. Professional painters typically charge between $2.00 and $4.50 per square foot of wall space, which includes prep work like masking, minor caulking, and cleanup.
Example Calculation
If you have a 12′ x 15′ room with 8′ ceilings, one door, and two windows:
- Gross Wall Area: 2 × (12 + 15) × 8 = 432 sq ft
- Subtractions: 21 (door) + 30 (2 windows) = 51 sq ft
- Net Area: 381 sq ft
- Paint Needed (2 coats): (381 × 2) / 350 ≈ 2.2 Gallons (Buy 3)
- DIY Cost: 3 gallons @ $45 = $135
- Pro Cost: $135 (paint) + (381 × $2.50) = $1,087.50