Paint Calculator
Estimate gallons of wall paint from room perimeter, wall height, openings, coats, and paint coverage.
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How this calculator works
Paintable area = perimeter × wall height − openings. Gallons = paintable area × coats ÷ coverage.
Worked example
A 64 ft perimeter room with 9 ft walls, 70 sq ft of openings, and two coats needs about 2.9 gallons at 350 sq ft/gal.
Measure paintable surface, not floor area
For walls, multiply room perimeter by wall height and subtract large doors and windows. Calculate ceilings separately. Closets, stairwells, textured surfaces, unfinished drywall, masonry, and dramatic color changes may require different coverage or primer.
The manufacturer’s spread rate is the best starting point. Application method, surface porosity, color, and painter technique can move actual coverage above or below the label estimate.
Plan coats and container sizes
Multiply the paintable area by the number of coats before dividing by coverage per gallon. Round up to purchasable container sizes and keep finish types separate. Do not combine wall, trim, ceiling, and primer quantities if they use different products.
Sources & assumptions
Paintable wall area subtracts entered openings and multiplies by the selected coats. Coverage is visitor-editable because surface texture, color change, application method, and product specifications affect spread rate.
Frequently asked questions
How much area does a gallon of paint cover?
Many interior paints are rated around 350 to 400 sq ft per gallon per coat. Check the specific product label.
Do I need primer?
Primer may be needed for bare surfaces, stain blocking, major color changes, or manufacturer requirements.
Room-by-room paint guide
Use the worked room examples and measurement checklist in How much paint do I need?