Paint Coverage Calculator
Gallons of paint needed for any wall area, with optional primer and second coat. Adjustable coverage rate for different paint types.
Paint needed
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Primer (gal)
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Net wall area
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ft²
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How to estimate paint
Gallons = (Wall area / Coverage per gallon) × Number of coats × (1 + Waste factor). Subtract significant openings: doors (~21 ft² each), standard windows (~15 ft² each). Don't bother subtracting tiny openings like switch plates or outlets.
Gallons = (Net wall ft² × coats × (1 + waste)) / Coverage rate
Typical coverage rates
- Interior latex paint: 300–400 ft² / gal
- Drywall primer: 250–300 ft² / gal
- Exterior latex: 300–400 ft² / gal
- Stain: 200–300 ft² / gal (varies wildly by wood absorbency)
- Concrete / masonry sealer: 200–400 ft² / gal
- Textured / heavy-bodied paint: 150–200 ft² / gal
Tips that save money
- Get to one gallon per 350 ft² minimum — don't over-thin or you'll need a third coat.
- Tint the primer halfway to the topcoat — it saves a coat of finish paint on big color shifts.
- Save the leftover quart with painter's tape under the lid; thinned 10% with water it stays usable 12+ months for touch-ups.
Frequently asked questions
How many gallons of paint do I need for a room?
Measure the total wall perimeter (sum of all wall lengths) and multiply by ceiling height for gross square footage. Subtract doors (~21 ft² each) and windows (~15 ft² each). Divide by the coverage rate (typically 350 ft²/gal for interior latex) and multiply by number of coats. Add 10% for waste. This calculator does all of that — just enter the perimeter length and height.
Does paint coverage rate vary between brands?
Yes, but only slightly. Most interior latex paints fall in the 300–400 ft²/gal range; premium thick-formula paints may claim 400 ft²/gal, while builder-grade paints are closer to 300. Porous or textured surfaces absorb more paint — use 200–250 ft²/gal for textured drywall, brick, or concrete block. The coverage rate on the can label is for smooth surfaces with two coats, which often overstates real-world yield.
When do I need primer before painting?
Prime when: painting bare drywall (paper face absorbs paint unevenly), doing a major color shift (dark to light), painting over stains or repairs, painting raw wood, or switching from oil-based to latex. Skip primer on previously painted walls in good condition where you're doing a minor color change in the same sheen. Tinting the primer halfway to the topcoat color reduces finish coats needed.
How many coats does a wall need?
Two coats is the standard for most wall painting — one for full coverage and one for even sheen. One coat is acceptable for touch-ups or very small color shifts. Three coats may be needed for drastic color changes (white over dark red, for example), unpainted drywall without primer, or textured surfaces that were spot-patched. Always let each coat fully dry before applying the next.
How do I estimate paint for a room without measuring every wall?
Use the perimeter method: walk the room and add up all the wall lengths to get the total perimeter, then multiply by the ceiling height. This is faster than measuring each wall individually and the result is the same. For a standard 12 × 14 ft bedroom with 9-ft ceilings, the perimeter is (12+14) × 2 = 52 ft, giving 52 × 9 = 468 ft² gross before subtracting openings.