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How to Calculate Paint Needed
Measure the total wall area by calculating the perimeter (2 x length + 2 x width) and multiplying by the wall height. Subtract the area of doors (approximately 21 sq ft each) and windows (approximately 15 sq ft each). Divide the paintable area by the paint coverage rate (typically 350 sq ft per gallon) and multiply by the number of coats.
Paint Coverage and Types
Most interior paints cover approximately 350-400 square feet per gallon on smooth surfaces. Textured surfaces, porous walls, or dark-to-light color changes may require more paint. Primer coats typically cover 200-300 sq ft per gallon. Always buy slightly more than calculated to account for touch-ups.
Tips for Accurate Paint Estimation
Measure each wall individually for irregularly shaped rooms. Account for ceiling paint separately. Consider that accent walls with different colors need their own calculation. Round up to the nearest gallon since partial gallons are rarely sold. Keep leftover paint for future touch-ups.
Frequently Asked Questions
A typical gallon of interior paint covers 350-400 square feet on smooth, primed surfaces. Coverage decreases on textured, unprimed, or porous surfaces. Check the paint can label for the manufacturer's specific coverage rate.
Two coats are generally recommended for even coverage, especially when changing colors. One coat may suffice with high-quality paint-and-primer combos over a similar existing color. Dark or bold colors often require a primer plus two coats.
Yes, subtract any area you will not paint. Standard closet doors are approximately 21 sq ft. If painting the closet interior, calculate that as a separate space with its own walls.
Buy 10-15% more paint than calculated to account for waste, spills, roller absorption, and future touch-ups. It is better to have extra paint than to run out mid-project and risk a color mismatch with a new batch.