How much paint do I need?
Find the paintable wall area, multiply by the number of coats, then divide by the coverage printed on the paint can. A typical gallon is often estimated at 350–400 square feet per coat, but texture, color change, product, and application method can reduce real coverage.
12 ft × 14 ft room
8-ft walls, 42 ft² of openings, two coats
The calculation
For a 12×14-foot room, the perimeter is 52 feet. With 8-foot walls, one standard door plus a 3×7-foot window (42 square feet total), two coats, and 350 square feet of coverage per gallon:
Paint is normally purchased in fixed container sizes, so round up in a way that matches the available cans. Keeping a small amount for touch-ups can also be useful.
Common room examples
These examples assume 8-foot walls, 42 square feet of doors and windows, two coats, and 350 square feet of coverage per gallon. Ceilings, trim, closets, and primer are not included.
| Room size | Paintable wall area | Calculated paint | Whole gallons |
|---|---|---|---|
| 10 × 10 ft | 278 ft² | 1.59 gal | 2 |
| 12 × 12 ft | 342 ft² | 1.95 gal | 2 |
| 12 × 14 ft | 374 ft² | 2.14 gal | 3 |
| 14 × 16 ft | 438 ft² | 2.50 gal | 3 |
These examples are planning estimates. Use the coverage stated for the exact primer and paint product.
Measure wall area—not floor area
For four walls, add the wall lengths to get the room perimeter, then multiply by wall height. Subtract substantial areas you will not paint, such as doors, windows, tile, cabinets, or large built-ins.
Rooms with sloped ceilings, stairwells, multiple wall heights, or many recesses are easier to measure as separate rectangles and triangles. Add their areas before applying the number of coats.
Use the product’s coverage rate
Sherwin-Williams says a gallon typically covers about 350–400 square feet, while also warning that wall texture and the desired coverage affect the amount needed. That range is a useful starting point, not a guarantee.
New drywall, porous masonry, rough texture, dramatic color changes, spraying, and product-specific application requirements can change spread rate. The label or technical data sheet for your selected product is the controlling source.
Paint, primer, ceiling, and trim are separate
- Wall paint: Use wall area × coats ÷ wall-paint coverage.
- Primer: Calculate separately using the primer’s own coverage rate. Sherwin-Williams gives 200–300 square feet per gallon as a typical primer range.
- Ceiling: For a simple flat ceiling, multiply room length by width, then apply coats and ceiling-paint coverage.
- Trim and doors: Estimate separately because the product, sheen, units, and application method may differ.
Frequently asked questions
Is one coat enough?
Sometimes, but two coats are commonly planned for even appearance and durability. Follow the product instructions, especially for major color changes or new surfaces.
Should I subtract every door and window?
Subtracting major openings improves the estimate. For a small project, leaving minor openings in the total can provide a modest cushion.
Why does the calculator round up?
You cannot buy 2.14 individual one-gallon cans. Rounding up helps avoid running short and can leave matching paint for touch-ups.