Paint Calculator
Paint Calculator
Wall area is perimeter x height, minus doors and windows. Coverage is usually 350 to 400 square feet per gallon, per coat, for interior latex paint. Primer is a separate coat, not counted as paint.
Estimate only. Densities, coverage and prices vary by supplier, quarry, moisture and region. Confirm the final order with your supplier before ordering.
A paint calculator counts wall area, coats, and gallons, with coverage per gallon, coats, and waste all changing the total. The most common paint mistake is counting floor area, not wall area, and forgetting ceilings, doors, and second coats, which can double the paint needed.
Use the free Square Footage Calculator for wall area, or work through the paint method below.
Paint calculator formulas
Coverage is usually 350 to 400 square feet per gallon, per coat, for interior latex paint, per manufacturer. Primer coverage is similar, but primer is a separate coat, not counted as paint.
Paint by surface
| Surface | Coverage per gallon, per coat | Coats |
|---|---|---|
| Interior walls, latex | 350 to 400 sq ft | 2 coats, plus primer if new |
| Ceilings, latex | 350 to 400 sq ft | 2 coats |
| Exterior walls, latex | 250 to 350 sq ft | 2 coats, plus primer if bare |
| Trim, doors | Smaller, by linear feet | 2 coats, brush and roller |
Worked example: 12 x 16 foot room, 8 foot ceilings, 2 coats
Perimeter: 12 + 12 + 16 + 16 = 56 feet. Wall area: 56 x 8 = 448 square feet, minus a 21 square foot door and a 15 square foot window, = 412 square feet net, before ceiling.
Gallons, walls only, 2 coats, 350 sq ft per gallon: 412 x 2 / 350 = 2.35 gallons, plus 10 percent waste = 2.59 gallons. Order 3 gallons, because paint is sold by gallon, not by fraction.
Ceiling, if painting it: 12 x 16 = 192 square feet, 2 coats, 192 x 2 / 350 = 1.10 gallons, plus waste = 1.21 gallons. Order 2 gallons for ceiling, separately, or 5 gallons total for walls plus ceiling, with primer extra if needed.
Paint by size, walls only, 2 coats, 350 sq ft per gallon, before waste
| Room size, 8 ft ceilings | Wall area, gross | Gallons, 2 coats |
|---|---|---|
| 10 x 10 ft | 320 sq ft | 1.83 gallons |
| 12 x 12 ft | 384 sq ft | 2.19 gallons |
| 12 x 16 ft | 448 sq ft | 2.56 gallons |
| 20 x 20 ft | 640 sq ft | 3.66 gallons |
Steps for planning paint
- Measure perimeter and height. For each room, separately, in feet.
- Subtract openings. Doors and windows over 10 square feet, before coats.
- Add ceiling, if painting it. Ceiling area is length times width, separately from walls.
- Multiply by coats, divide by coverage. Use manufacturer coverage, not a generic number, for the final order.
- Round up to gallons, add primer separately. Paint is sold by gallon, primer is a separate product and coat.
Related calculators and guides
Wall and ceiling area, before paint.
Flooring Calculator
Flooring area, waste, and boxes.
Tile Calculator
Tile area, waste, and boxes.
Brick Calculator
Bricks, mortar, and waste for walls.
Lumber Buying Guide
Timber for trim and framing.
Board Foot Calculator
For timber trim and framing.
Frequently asked questions
How much paint for a 12 x 16 room?
Walls only, 2 coats, 350 sq ft per gallon: about 2.56 gallons gross, about 2.82 with waste, order 3 gallons. Ceiling adds about 1.21 gallons with waste, order 2 gallons separately.
How many square feet does a gallon of paint cover?
Usually 350 to 400 square feet per gallon, per coat, for interior latex paint, per manufacturer. Exterior and textured surfaces cover less.
How many coats of paint do I need?
Usually 2 coats of paint, plus primer if the surface is new, bare, or a drastic colour change.
Should I subtract doors and windows for paint?
Yes, subtract openings over 10 square feet, before coats. Small openings can be kept in as waste, if you say so.
Do I need primer?
Yes for new drywall, bare wood, stains, and drastic colour changes. No, usually, for repainting a similar colour on a sound, previously painted surface.
How much waste for paint?
10 percent for cutting in, roller loss, and touch-ups. More for textured surfaces, spray application, or complex trim.
Estimate only. Confirm coverage per gallon and coats with your paint manufacturer before ordering.