Paint Calculator
Estimate the gallons of paint you need for interior rooms or exterior walls. Includes primer calculations and costs.
How to Calculate Paint Needed for Your Project
Estimating paint accurately saves money and prevents multiple store trips. The basic approach is to calculate the square footage of walls you need to paint, account for doors and windows, then factor in the number of coats and coverage rate per gallon. Adding a waste factor (typically 5-15%) ensures you have enough paint for touch-ups and variations in surface absorption.
Paint Coverage Rates
Most interior paints cover 350-400 square feet per gallon, though this depends on surface texture and paint quality. Flat or matte finishes typically provide more coverage than glossy finishes. Primers generally cover 350-400 sq ft per gallon as well. On textured or stucco surfaces, expect coverage to drop to 250-300 sq ft per gallon. Always check your specific paint can for the manufacturer's coverage recommendations.
Calculating Paint Needed: Step by Step
Start by measuring the perimeter of your room and multiply by ceiling height to get total wall area. For example, a 12x14 room with 8-foot ceilings has a perimeter of 52 feet, resulting in 416 square feet of wall space. Subtract 20 sq ft per door and 15 sq ft per window to get your paintable area. Multiply by the number of coats you plan to apply, then add 10% for waste, giving you 459 square feet. Finally, divide by your paint's coverage rate (350 sq ft) to determine 1.3 gallons needed.
Interior vs Exterior Paint Differences
Interior paints are formulated for low-VOC performance and easy cleanup, while exterior paints contain additives for weather resistance, UV protection, and mildew prevention. Exterior paints are typically more expensive and durable. Additionally, exterior walls often have more surface variation and may require extra primer, reducing overall coverage. Always use paint specifically designed for your application — interior paint on exterior surfaces will fade and fail quickly in sun and moisture.
Tips for Estimating Paint Quantities
- Two coats are standard for most projects and provide better coverage
- Always prime if painting over a significantly different color or new drywall
- Add an extra 5-15% for waste, spillage, and touch-ups after drying
- Textured or porous surfaces require more paint than smooth finishes
- Lighter colors typically require more coats than darker shades
- Buy paint in the quantity you calculate plus one extra gallon for future touch-ups
Common Interior Painting Projects
A typical bedroom (12x14 with 8-ft ceilings) needs about 1.5-2 gallons for two coats. A living room (20x16) requires approximately 3-4 gallons. A full house interior might require 15-20 gallons depending on layout and color changes. When painting exteriors, a single-story 2,000 sq ft home typically needs 8-12 gallons for two coats, while a two-story home may require 12-18 gallons.