How Much Paint Do I Need
How Much Paint Do I Need comes down to one formula: paintable square footage ÷ 350 sq ft per gallon × number of coats, plus about 10% for waste. One gallon of quality interior paint covers 350–400 sq ft in a single coat on smooth, previously painted walls, so a typical 12x12 bedroom needs about 1.5–2 gallons for two coats on the walls. This article works the math step by step, gives look-up tables for common room sizes, and explains when coverage drops well below the number on the can.
The Coverage Formula
- Measure the perimeter. Add the lengths of all walls. A 12x12 room = 48 linear feet.
- Multiply by ceiling height. 48 ft × 8 ft = 384 sq ft of gross wall area.
- Subtract openings. Deduct about 20 sq ft per door and 15 sq ft per average window. Two doors and two windows: 384 − 70 = 314 sq ft. (Skip this step if openings are small — the margin becomes your waste factor.)
- Divide by coverage. 314 ÷ 350 = 0.9 gallons per coat.
- Multiply by coats. Two coats: 1.8 gallons. Buy two gallons.
Use 350 sq ft/gallon as your planning number even though many cans claim 400. Real-world coverage on roller-applied paint, with cut-in overlap and tray residue, lands closer to 300–350. On rough texture, unprimed drywall, or masonry, budget 250–300 sq ft/gallon. Painting Brick, Painting Concrete, and Painting Stucco surfaces can drink 200 sq ft/gallon or less on the first coat.
Paint Needed by Room Size
Figures assume 8-foot ceilings, average doors/windows, and two coats on walls. Round up to whole gallons — leftover paint is touch-up insurance.
| Room | Approx. Wall Area | Walls (2 coats) | Ceiling (1 coat) | Trim |
|---|---|---|---|---|
| 10x10 bedroom | 260 sq ft | 1.5 gal (buy 2) | 100 sq ft — 1 quart–½ gal | 1 quart |
| 12x12 bedroom | 315 sq ft | 1.8 gal (buy 2) | 144 sq ft — ½ gal | 1 quart |
| 12x14 bedroom | 345 sq ft | 2 gal | 168 sq ft — ½ gal | 1 quart |
| 14x16 living room | 410 sq ft | 2.3 gal (buy 3) | 224 sq ft — 1 gal | 1–2 quarts |
| 15x20 great room (9 ft ceilings) | 560 sq ft | 3.2 gal (buy 4) | 300 sq ft — 1 gal | 2 quarts |
| 10x12 kitchen (walls above cabinets) | 200 sq ft | 1.2 gal (buy 2) | 120 sq ft — ½ gal | 1 quart |
| 8x10 bathroom | 200 sq ft | 1.2 gal (buy 2) | 80 sq ft — 1 quart | 1 quart |
Whole-House Estimates
| Home Size | Interior Walls (2 coats) | Ceilings (1 coat) | Trim and Doors |
|---|---|---|---|
| 1,000 sq ft | 6 gal | 3 gal | 1–2 gal |
| 1,500 sq ft | 8–10 gal | 4 gal | 2 gal |
| 2,000 sq ft | 11–13 gal | 5–6 gal | 2–3 gal |
| 2,500 sq ft | 14–16 gal | 6–7 gal | 3 gal |
| 3,000 sq ft | 17–20 gal | 7–8 gal | 3–4 gal |
A rule of thumb for interior work: wall area ≈ floor area × 2.5–3 in a typical layout. Exterior estimates run differently — siding texture, vinyl, and lap boards add 10–50% to plain wall math.
How Many Coats?
- Two coats is the default for uniform color and full sheen development, even with "one-coat" paints.
- One coat can work when repainting the same color with the same sheen for freshening.
- Three coats (or two over tinted primer) for deep reds, bright yellows, and going light-over-dark. Tinting the primer gray toward the topcoat color usually saves a full coat of expensive paint.
- Darker existing colors, patched drywall, and glossy surfaces all push you toward the higher coat count. Higher-sheen paints show lap marks more, which also favors two full coats.
Primer and the Waste Factor
Primer covers 200–300 sq ft per gallon — less than paint, because it is formulated to soak in and seal. New drywall, stain-blocking, and painting over wallpaper all call for a dedicated primer coat; figure one gallon of primer per 250 sq ft.
Add a 10% waste factor to every calculation. Paint stays in the tray, loads the roller, dries in the bucket, and gets used for drips and touch-ups. On small jobs the rounding to whole gallons usually absorbs this; on whole-house jobs, add an actual extra gallon per 10 you buy. Buying all gallons of a custom tint at once (or having the store box them — intermix into one container) prevents can-to-can tint variation.
Budget-wise, expect $30–$60 per gallon for mid-range interior latex and $70–$100 for premium lines in 2026; see How Much Does Painting Cost for full project budgeting. Leftovers keep 2–10 years sealed — and when they finally go bad, follow Paint Disposal rather than the drain.
Common Mistakes
- Trusting the 400 sq ft/gallon can rating on textured or porous walls and running out mid-wall.
- Forgetting the second coat in the math — the single most common reason people buy half enough.
- Buying custom-tinted gallons one at a time; slight tint differences show as bands on large walls.
- Skipping primer on a drastic color change and paying for a third and fourth coat of premium paint instead.
- Not deducting a huge feature like a stone fireplace or full-wall built-ins, then over-buying by gallons.
- Estimating ceiling paint from wall math — ceilings are simply length × width, one coat in most cases.
Frequently Asked Questions
How much paint do I need for a 12x12 room?
About 1.5–2 gallons for two coats on the walls, assuming 8-foot ceilings and average doors and windows (roughly 315 sq ft of wall area). Add a half gallon of flat ceiling paint for the 144 sq ft ceiling and a quart of enamel for trim. Buy two gallons of wall paint so you have touch-up left over.
How many square feet does a gallon of paint cover?
Manufacturers rate most interior paints at 350–400 sq ft per gallon per coat. Plan on 350 for smooth previously painted walls, 250–300 for texture, raw drywall, or masonry, and as little as 200 for the first coat on rough brick or stucco. Primer covers less — about 200–300 sq ft per gallon.
Is one gallon of paint enough for a bedroom?
Only for a small bedroom in one coat. A 10x10 bedroom has about 260 sq ft of wall area, so one gallon covers a single coat with little to spare — and two coats is the standard for even color. For any bedroom 10x10 or larger, buy two gallons.
How much paint do I need for a 2,000 square foot house?
Roughly 11–13 gallons for two coats on all interior walls, plus 5–6 gallons of ceiling paint and 2–3 gallons of trim enamel — about 18–22 gallons total. Exteriors of the same footprint typically need 10–15 gallons depending on siding texture and color change.
Do I calculate paint differently for ceilings and trim?
Yes. Ceilings are length × width and usually get one coat of dedicated flat ceiling paint. Trim is estimated by linear feet: one quart of enamel covers roughly 250 linear feet of baseboard or casing per coat, and a standard door takes about a fifth of a quart per coat. See Painting Trim and Painting Doors.
