Paint Coverage Calculator
Determine how many gallons of paint you need for walls based on room dimensions, doors, windows, coats, and coverage rate.
Enter room dimensions and click calculate.
What This Calculator Does
This calculator determines how many gallons of paint are needed to cover the walls of a room. It accounts for room dimensions, wall height, doors, windows, number of coats, and the paint coverage rate to produce an accurate gallon estimate and material cost.
The Formula
Total wall area is the room perimeter multiplied by ceiling height. Standard doors (3x7 ft = 21 sq ft) and windows (3x5 ft = 15 sq ft) are subtracted since they are not painted. The paintable area is multiplied by the number of coats, then divided by the coverage rate (typically 350-400 sq ft per gallon for smooth walls).
Step-by-Step Example
Measure the room
Record length, width, and wall height. Example: 15 ft x 12 ft room with 9 ft ceilings.
Count doors and windows
Standard door = 21 sq ft deduction. Standard window = 15 sq ft deduction. Example: 2 doors, 2 windows.
Select coats and coverage rate
Most paint jobs need 2 coats. Coverage is typically 350 sq ft/gallon for smooth drywall, 300 sq ft/gallon for textured surfaces.
Review gallon estimate
For the example room: 486 sq ft walls - 72 sq ft openings = 414 sq ft. With 2 coats at 350 sq ft/gal = 3 gallons.
Real-World Use Cases
Painting Contractor Estimates
Calculate material quantities for multiple rooms in a residential or commercial paint job to build accurate bids.
DIY Project Planning
Buy the right amount of paint on the first trip to the store and avoid excess or shortages.
Property Management
Estimate repainting costs for unit turnovers and budget for annual maintenance.
Common Mistakes to Avoid
Forgetting to multiply by the number of coats. One coat rarely provides adequate coverage, especially when changing colors dramatically.
Using the manufacturer maximum coverage rate. Real-world coverage is lower due to surface texture, porosity, application method, and color change.
Not deducting doors and windows, which can overestimate paint needs by 10-15% in rooms with multiple openings.
Ignoring ceiling paint if ceilings are also being painted. Ceiling area equals length times width.
Frequently Asked Questions
Accuracy and Disclaimer
Paint coverage varies based on surface texture, porosity, application method (roller vs. spray vs. brush), paint quality, and color change severity. This calculator uses standard assumptions. Consult with your paint supplier for specific product coverage rates.
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