Paint Calculator
Calculate the amount of paint needed for interior walls based on room dimensions and openings. This calculator accounts for doors, windows, and multiple coats to give you accurate estimates.
How to Calculate Paint Needed
Calculating paint requirements accurately saves money and prevents multiple trips to the store. Here's how the calculation works and what factors to consider.
Basic Paint Formula
Paint Needed = (Wall Area - Doors - Windows) x Number of Coats / Coverage Rate
Most interior paints cover about 350-400 square feet per gallon on smooth surfaces. Textured walls or porous surfaces may reduce coverage by 25-30%.
Step-by-Step Calculation
- Measure the room: Length, width, and ceiling height
- Calculate wall area: 2 x (length x height) + 2 x (width x height)
- Subtract openings: Doors (20 sq ft each) and windows (15 sq ft each)
- Multiply by coats: Usually 2 coats for best results
- Divide by coverage: 350 sq ft per gallon is standard
Coverage Rates by Paint Type
- Premium paint: 400-450 sq ft per gallon
- Standard paint: 350-400 sq ft per gallon
- Primer: 300-350 sq ft per gallon
- Textured surfaces: Reduce coverage by 25%
Professional Painting Tips
Before You Buy Paint
- Always buy 10-15% extra for touch-ups and future repairs
- Buy all paint at once to ensure color consistency
- Consider paint quality - premium paints often cover better in fewer coats
- Check if primer is needed for new drywall or dramatic color changes
When You Need Primer
- Painting over dark colors with light colors
- New drywall or unpainted surfaces
- Covering stains, crayon marks, or water damage
- Switching from oil-based to latex paint
Surface Preparation
- Clean walls with mild detergent and let dry completely
- Fill nail holes and cracks with spackling compound
- Sand glossy surfaces lightly for better paint adhesion
- Use high-quality painter's tape for clean lines
Application Tips
- Use a high-quality brush for cutting in edges and corners
- Roll paint in a "W" pattern, then fill in with parallel strokes
- Maintain a wet edge to avoid lap marks
- Apply thin, even coats rather than one thick coat
Cite this page as:
Daniel, P. Paint Calculator. Available at: https://constructioncalculators.com/paint-calculator/. Accessed: October 25, 2026.