Paint Coverage Calculator

Calculate how much paint you need for a room from its dimensions, openings, coats, and a touch-up reserve.

Paint Needed
— gallons
Includes touch-up reserve.

Usage Tip

Buy all your paint in one batch and box it together (mix the cans) so the color stays consistent across the whole room.

THE MATH
wall area = 2 × height × (length + width) − doors × 21 − windows × 15
gallons = wall area × coats ÷ coverage × (1 + reserve)
Paintable wall area is the room perimeter times the ceiling height, minus the door and window openings. Gallons follow from the coverage rate, the coats, and a touch-up reserve.
Enter the room dimensions, the door and window counts, the coats, the surface coverage rate, and a touch-up reserve.
Doors count as 21 square feet and windows as 15.
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.