Free paint coverage calculator.
This free paint coverage calculator returns the gallons of paint needed for a room, with optional primer, waste-adjusted and rounded up to whole gallons. Tunable coverage rate for rough vs smooth surfaces. Output in US gallons and liters. Imperial or Metric.
Paint needed
1 US gallon ≈ 3.79L. Round up to whole gallons for purchase; suppliers don't sell fractional gallons.
Want this measured straight from your PDF instead? BidScreen XL adds the same math to Microsoft Excel — trace the drawing, the quantity lands as a live cell.
Area × coats ÷ coverage.
Wall area is the room's perimeter times the ceiling height. A 12 × 14 ft room at 8 ft is 2 × (12 + 14) × 8 = 416 ft². Subtract a flat percent for openings (10% typical) to get the paintable area.
Multiply paintable area by the number of coats, then divide by the coverage per gallon. 416 × 2 ÷ 350 ≈ 2.4 gal. Round up to whole gallons because suppliers don't sell fractional quantities.
For primer, run the same math with the primer's own coverage (≈ 250 ft²/gal for drywall primer). Don't skip primer on new drywall — the paper face soaks paint and you'll burn through two coats trying to get the wall to cover.
Frequently asked
How many square feet does a gallon of paint cover?
350 ft² per gallon on smooth drywall in one coat is the manufacturer's typical claim and a sensible default. Rough or porous surfaces (stucco, concrete block, raw drywall) drop coverage to 200-250 ft²/gal. Smooth painted surfaces being recoated cover at the high end (350-400 ft²/gal).
Do I need two coats?
Yes, almost always. One coat rarely achieves full color hide unless the paint is the same color over a similar primer. Default to two coats for any color change; three coats for deep saturated colors over white or vice versa.
When do I need primer?
New drywall: 1 coat of drywall primer to seal the paper face. Stained or repaired surfaces: 1 coat of stain-blocking primer over the affected areas. Drastic color change (dark over light, or red/orange over neutral): 1 coat of tinted primer matched to the topcoat. Otherwise, skip primer and run an extra coat of paint.
How do I handle ceilings or trim?
Run the calculator twice: once for walls with wall paint, once for ceiling with ceiling paint. Trim (baseboards, casing) is usually small enough to bundle into a single quart per gallon of trim paint per room.
Should I subtract doors and windows?
Yes — the openings allowance does this. 10% covers a typical residential room with one or two doors and a window or two. 15% for rooms with full-wall windows; 5% for a windowless garage. The calculator subtracts a flat percent of wall area, which is accurate enough for paint quantity.
BidScreen XL traces every wall on the plan.
For multi-room paint jobs, BidScreen XL traces each wall's linear footage on the floor plan, multiplies by ceiling height, and pulls the wall area straight into your Excel paint estimate as a live formula.