Paint Coverage Calculator: How Many Gallons Do You Need for Any Room?

## The Mistake That Sends Everyone Back to the Store You buy two gallons, paint the room, and run out at the last wall. Or you buy five gallons and return three unopened cans — except the store won't take back custom-tinted paint. Getting the paint quantity right before you start saves a second trip, avoids color mismatch between cans, and means you don't end up with a half-finished wall drying to a different shade. Our [paint coverage calculator](/category/construction/paint-coverage-calculator) gives you the exact gallon count. This guide explains the math and the factors that change it. --- ## The Formula **Gallons needed = Paintable area ÷ Coverage rate per gallon** Most interior latex paint covers **350–400 sq ft per gallon** on a smooth, primed surface. Premium paints and self-priming formulas are typically at the lower end (300–350 sq ft) because they're thicker. ### Standard Coverage Rate by Paint Type | Paint Type | Coverage per Gallon | |------------|--------------------| | Standard latex (interior) | 350–400 sq ft | | Premium / self-priming | 300–350 sq ft | | Chalk paint | 150–200 sq ft | | Exterior paint | 300–400 sq ft | | Primer | 200–300 sq ft | | Spray paint (rattle can) | 20 sq ft | For your calculation, use **350 sq ft/gallon** as a conservative default — you'll have a small buffer without excessive waste. --- ## Calculating Wall Area **Wall area = (2 × Room length + 2 × Room width) × Ceiling height** Then subtract doors and windows: - Standard door: 21 sq ft (3 ft × 7 ft) - Standard window: 15 sq ft (3 ft × 5 ft) ### Worked Example: 12×14 Room, 9-ft Ceiling, 1 Door, 2 Windows - Perimeter: (2×12) + (2×14) = 52 linear ft - Wall area: 52 × 9 = **468 sq ft** - Less 1 door: −21 sq ft - Less 2 windows: −30 sq ft - **Net paintable area: 417 sq ft** At 350 sq ft/gallon: 417 ÷ 350 = **1.19 gallons per coat** For **2 coats** (standard): 1.19 × 2 = **2.38 gallons → buy 3 gallons** [Calculate your exact paint quantity →](/category/construction/paint-coverage-calculator) --- ## How Many Coats Do You Need? The number of coats changes your total dramatically. | Situation | Coats Needed | |-----------|--------------| | Same color, good condition | 1–2 | | New drywall (primed) | 2 | | Dark to light color change | 3 (prime + 2 coats) | | Light to dark color change | 2 | | Unprimed drywall | Prime + 2 coats | | Heavily textured surface | 2–3 (more surface area) | | Glossy surface without sanding | Adhesion primer + 2 coats | **Going from white to dark red or navy?** Budget for a tinted primer coat first — it reduces the number of topcoat layers needed from 3–4 down to 2. --- ## Ceiling Paint Ceiling paint covers the same area formula: length × width. For a 12×14 room: 12 × 14 = **168 sq ft** At 350 sq ft/gallon for 2 coats: 168 × 2 ÷ 350 = **0.96 gallons → buy 1 gallon** Ceiling paint is typically flat white and sold separately from wall paint. One gallon handles most bedrooms and living rooms in two coats. Buy a second gallon for open-plan spaces over 300 sq ft. --- ## Trim, Doors, and Baseboards Trim is measured by linear foot, not square foot. A rough coverage estimate: - 1 gallon of trim paint covers approximately **600–800 linear feet** of baseboard (3.5 in wide) - Standard door (both sides + edges): ~1 quart covers 2–3 doors - Window casing: similar to doors For a typical bedroom with 50 linear feet of baseboard and 1 door: - Baseboard: 50 ÷ 700 = 0.07 gallons - Door: ~0.25 quart - **Buy 1 quart of trim paint** --- ## Texture and Surface Condition: The Hidden Variable The 350 sq ft/gallon figure assumes a smooth, properly prepared surface. Real surfaces vary: | Surface Type | Adjustment | |-------------|------------| | Smooth primed drywall | Baseline (350 sq ft/gal) | | Eggshell or satin finish | −10% coverage | | Knockdown or orange peel texture | −15 to −20% | | Heavy popcorn texture | −25 to −35% | | Bare (unprimed) drywall | Use primer first; loses 25% to absorption | | Bare wood | −30 to −40% (very absorbent) | | Previously glossy surface, not sanded | Poor adhesion — use bonding primer | A heavily textured wall has significantly more actual surface area than its flat footprint suggests. If your room has knockdown texture throughout, bump your gallon estimate up by 20%. --- ## The Full Room Paint Shopping List For the 12×14 room example (2 coats walls, 2 coats ceiling, 1 coat trim): | Item | Quantity | Notes | |------|----------|-------| | Wall paint | 3 gallons | 417 sq ft × 2 coats ÷ 350 = 2.38, round up | | Ceiling paint | 1 gallon | 168 sq ft × 2 coats ÷ 350 = 0.96, round up | | Trim paint | 1 quart | Baseboard + 1 door | | Primer (if needed) | 1 gallon | 400 sq ft for new drywall | **Total: 3 gallons wall + 1 gallon ceiling + 1 quart trim + 1 gallon primer (if needed)** Buying in gallons vs. quarts: a gallon is always cheaper per square foot than buying quarts. Only buy quarts when you need less than 1 gallon total — accent walls, small bathrooms, or touch-up work. --- ## Exterior Paint: Key Differences Exterior paint calculation uses the same formula, but with different variables: - **Siding coverage**: measure the building perimeter × height, subtract windows and doors - **Coverage rate**: 300–400 sq ft/gallon (slightly less than interior due to texture) - **Coats**: 2 coats minimum on new or bare wood; 1–2 coats on previously painted in good condition - **Trim**: measure linear footage and calculate separately For an average 1,500 sq ft ranch house exterior: - Siding area: ~1,200 sq ft (after deducting windows and doors) - 2 coats: 1,200 × 2 ÷ 350 = **6.9 gallons → buy 7 gallons** of exterior paint --- ## Related Construction Calculators - [Tile Calculator](/category/construction/tile-quantity-calculator) — how many tiles for any floor or wall - [Drywall Calculator](/category/construction/drywall-calculator) — sheets and screws for any room - [Deck Calculator](/category/tools/deck-calculator) — lumber, posts, and concrete for any deck - [Concrete Calculator](/category/construction/concrete-calculator) — bags for any pour --- ## Frequently Asked Questions **How many gallons of paint do I need for a 12×12 room?** Wall area: (4 walls × 12 ft) × 8 ft ceiling = 384 sq ft. Less 1 door and 1 window ≈ 348 sq ft net. For 2 coats at 350 sq ft/gallon: 348 × 2 ÷ 350 = **2.0 gallons**. Buy 2 gallons with a small buffer. **Does one gallon of paint cover 400 sq ft?** On a smooth, primed surface, yes — most standard latex paints cover 350–400 sq ft per gallon per coat. On rough texture, bare drywall, or dark existing colors, expect 250–300 sq ft per gallon. **How much paint do I need for one wall?** Measure height × width of the wall in feet. Divide by 350 (sq ft per gallon) and multiply by the number of coats. A standard 8×12 ft wall = 96 sq ft × 2 coats ÷ 350 = **0.55 gallons → buy 1 quart (0.25 gal) × 2 or 1 half-gallon**. **Should I buy extra paint?** Always buy one extra quart beyond your calculated need for touch-ups. Store it sealed in a climate-controlled space — properly stored latex paint lasts 10 years. Label the can with the room name and the paint color code for easy reorder.