One gallon of paint covers about 350 to 400 square feet in a single coat, but nearly every job needs two coats and most need primer as well. This calculator works from room dimensions to a gallon count that reflects how paint actually gets used.
Painting new drywall? Check sheet counts with the Drywall Calculator first.
About pricing on this page
This calculator is intentionally price-light. Absolute dollar figures are deliberately omitted because they vary too widely by region, brand, and installer to be useful as planning estimates. The relative-comparison tables below show how options stack up against each other — which is the durable, actionable information. For a real budget, get two or three written quotes from local suppliers and contractors after they have seen the job.
Paint Quantity Calculator
Enter room dimensions, number of coats, and coverage rate. Results give gallons for walls and ceiling.
The Paint Coverage Formula
Wall Area = ((Length + Width) × 2) × Ceiling Height − Openings
Gallons = (Wall Area × Coats) ÷ Coverage per Gallon
Worked example: A 14 × 12 ft bedroom with 8 ft ceilings, one door and two windows. Perimeter is 52 ft, so walls are 52 × 8 = 416 sq ft. Subtract 42 sq ft for openings: 374 sq ft. Two coats at 400 sq ft per gallon: (374 × 2) ÷ 400 = 1.87 → 2 gallons. The 168 sq ft ceiling needs another 1 gallon for two coats.
Coverage claims on the can assume a smooth, primed, mid-tone surface. Real-world coverage on textured or previously unpainted drywall runs 15–30% lower, so the second coat carries more of the job than most people expect.
Paint Needed by Room Size
Figures assume 8 ft ceilings, two coats at 400 sq ft per gallon, and 42 sq ft deducted for a door and two windows.
| Room Size | Wall Area | Wall Gallons | Ceiling Area | Ceiling Gallons | Total Gallons |
|---|---|---|---|---|---|
| 8 × 10 ft | 246 sq ft | 1.5 | 80 sq ft | 0.5 | 2 |
| 10 × 12 ft | 310 sq ft | 1.6 | 120 sq ft | 0.6 | 3 |
| 12 × 12 ft | 342 sq ft | 1.7 | 144 sq ft | 0.7 | 3 |
| 12 × 14 ft | 374 sq ft | 1.9 | 168 sq ft | 0.8 | 3 |
| 14 × 16 ft | 438 sq ft | 2.2 | 224 sq ft | 1.1 | 4 |
| 16 × 20 ft | 534 sq ft | 2.7 | 320 sq ft | 1.6 | 5 |
| 20 × 24 ft | 662 sq ft | 3.3 | 480 sq ft | 2.4 | 6 |
Always round up to whole gallons, and buy all your paint in one order so it comes from the same tint batch. Color mixed weeks apart can differ subtly but visibly on a large wall.
Paint Coverage by Surface Condition
Surface porosity is the biggest variable in real coverage. New drywall drinks paint; previously painted smooth walls do not.
| Surface | Coverage per Gallon | Primer Needed? | Recommended Coats |
|---|---|---|---|
| Previously painted, same color | 400–450 sq ft | No | 1 |
| Previously painted, similar tone | 375–400 sq ft | No | 2 |
| Previously painted, dark to light | 350 sq ft | Yes | 2–3 |
| New drywall (primed) | 350–400 sq ft | Already primed | 2 |
| New drywall (unprimed) | 250–300 sq ft | Yes — PVA primer | 2 |
| Light texture (orange peel) | 325–375 sq ft | No | 2 |
| Heavy texture (knockdown) | 250–300 sq ft | No | 2 |
| Bare wood trim | 300–350 sq ft | Yes | 2 |
| Stained or water-damaged | 300 sq ft | Yes — stain blocking | 2 |
Paint Cost by Quality Tier
| Tier | Price per Gallon | Coverage | Durability | Best For |
|---|---|---|---|---|
| Builder / contractor grade | Reference only | 350 sq ft | 3–5 yr | Rentals, quick flips, ceilings |
| Mid-range | Reference only | 375–400 sq ft | 7–10 yr | Most interior rooms |
| Premium | Reference only | 400–450 sq ft | 10–15 yr | High-traffic, kitchens, baths |
| Designer / specialty | Reference only | 375–400 sq ft | 10–15 yr | Deep colors, specific finishes |
| PVA primer | Reference only | 300–350 sq ft | — | New drywall sealing |
| Stain-blocking primer | Reference only | 250–300 sq ft | — | Water stains, smoke, knots |
Premium paint frequently covers in two coats where builder grade needs three, so the higher per-gallon price often produces a lower total project cost once labor is included.
Common Paint Estimating Mistakes
Buying for One Coat
The coverage figure on the can is per coat, and almost every job needs two. Buying 2 gallons for a 700 square foot job based on a 350 sq ft coverage claim leaves you exactly half short. Multiply your area by the number of coats before dividing by coverage — that single step is where most shortfalls originate.
Skipping Primer on New Drywall
Unprimed drywall and joint compound absorb paint at very different rates, so the finish coat dries with visible flashing wherever a taped seam sits. A coat of PVA primer seals both surfaces uniformly and usually avoids a third finish coat. PVA primer is also cheaper per square foot than finish paint and saves labour time on the top coat.
Deducting Every Window and Door
Subtracting each small opening precisely leaves you short in practice, because you still roll and cut around every frame and the tray loses paint at each refill. Deduct about 21 sq ft for a standard door and 15 sq ft for an average window, then leave it there. Very small openings are best ignored entirely.
Using Wall Paint on the Ceiling
Ceiling paint is formulated flatter and thicker specifically to hide imperfections and resist spatter while rolling overhead. Wall paint on a ceiling shows every roller lap under raking light, and it drips on you while you work. Ceiling paint is also usually cheaper, so there is no advantage to substituting.
About these price ranges
Pricing varies widely by region, season, project size, and site conditions. Treat every figure on this page as a planning estimate for budgeting only — not as a quote. Coastal metro markets commonly run 20–40% above national ranges while rural inland markets can fall 10–20% below. Always collect at least three written quotes from local contractors before committing to a budget.
Unsourced estimates: All dollar figures on this page. The relative-comparison tables above are sourced from general trade conventions and the labour-plus-material methodology used in industry references, not from a specific published price index. These are informed planning figures rather than data drawn from a published price index, and they carry a correspondingly wider margin of error.