Paint Coverage Calculator

Calculating paint for a room involves measuring the wall area and accounting for your number of coats. Step-by-step calculation: measure the room. Measure the perimeter (total length of all walls). Example: 12 × 14 ft room = perimeter of (12 + 14) × 2 = 52 feet. Multiply by ceiling height. 52 ft × 8 ft ceiling = 416 sq ft of wall area. Subtract doors and windows. Subtract about 20 sq ft per standard door and 15 sq ft per average window. Example: 2 doors + 2 windows = (2 × 20) + (2 × 15) = 70 sq ft subtracted. Net area: 416 − 70 = 346 sq ft. Divide by coverage rate. Standard interior paint covers ~350–400 sq ft per gallon. 346 sq ft ÷ 350 sq ft/gal ≈ 1 gallon for one coat. Multiply by number of coats. Two coats = 1 gallon × 2 = 2 gallons. Add 10% for waste and touch-ups. 2 gallons × 1.10 = 2.2 gallons → buy 2 quarts (0.5 gal each) or a second gallon. Quick room estimates (standard 8 ft ceilings, 2 coats): small bedroom (10×10): ~1.5 gallons. Average bedroom (12×12): ~2 gallons. Large bedroom (14×16): ~2.5 gallons. Living room (16×20): ~3.5 gallons. Important notes: ceilings are a separate calculation — add 1 gallon per 300–400 sq ft of ceiling. Trim and doors are typically done with a separate semi-gloss paint and can usually be done with 1 quart for most rooms. Rough or porous surfaces (unprimed drywall, textured walls, exterior rough siding) need significantly more paint — up to 50% more.

The number of coats depends on the starting condition, the color change, and the surface type. Minimum coats by scenario: repainting same color (or very similar): usually 1 coat is enough for touch-up; 2 coats for a complete fresh look. Different color, similar value (neither very light nor very dark): 2 coats is standard. Light color over dark: this is the challenging scenario. 3–4 coats of the light color may still show the dark color bleeding through. Better approach: use a gray or mid-tone primer matched to the new color. Then apply 2 coats of finish paint. Total: primer + 2 coats. This typically gives better results with fewer coats than applying 3–4 straight finish coats. Dark color over light: 2 coats usually gives solid coverage. New drywall (even if primed): 2 coats minimum. New drywall without primer: 3 coats. Don't skip primer on bare drywall — without it, the drywall paper absorbs the first coat unevenly, leaving a blotchy finish called "flashing." Bare wood: 1 coat primer + 2 coats finish minimum. Exterior painting: 2 coats always. Trim, cabinets, and high-traffic areas: 2 coats minimum; 3 for heavy-use surfaces. Paint quality matters: high-quality paints (Benjamin Moore Aura, Sherwin-Williams Emerald) often deliver better coverage in fewer coats. Premium paint at 2 coats may perform better than budget paint at 3 coats — and the cost difference is often minimal per square foot.

The short answer: sometimes, but often less than the label claims. The 350–400 sq ft per gallon figure is the manufacturer's theoretical coverage under ideal conditions: smooth, properly prepared, primed surface. Single coat applied at correct spread rate. Professional application technique. Real-world factors that reduce coverage significantly: surface texture: rough or porous surfaces can reduce coverage to 150–250 sq ft/gallon. Rough stucco, brick, or textured ceilings can absorb dramatically more paint. Brush vs. roller vs. sprayer: rolling typically applies 25–30% more paint per pass than manufacturer testing assumes. Heavier application = lower coverage. Spraying: can extend or reduce coverage depending on distance and technique. Porous surfaces (new drywall, bare wood): the first coat is heavily absorbed. Coverage may be 200 sq ft or less for a first coat on bare drywall. Color: darker, richer colors (especially deep reds and dark blues) have lower coverage because they require more pigment. These may cover 250–300 sq ft/gallon. Old, chalky, or damaged surfaces: more paint is absorbed into the substrate. Paint quality: budget paints have lower pigment load and cover less area per coat. So what's the practical number? For a smooth, previously painted interior wall in good condition with quality paint: 350–400 sq ft/gallon is realistic. For rough, porous, or problematic surfaces: plan for 250–300 sq ft/gallon. For textured ceilings (popcorn): 100–150 sq ft/gallon. Rule of thumb: buy 10–15% more paint than your calculation suggests. Leftover paint stores well (2–10 years) for touch-ups and is much cheaper than running short mid-project.

Primer is not always required, but it's almost always beneficial and sometimes essential. When you MUST prime: new drywall: the paper facing of drywall is extremely absorbent. Without primer, finish paint soaks in unevenly, creating "flashing" — areas that look duller or have different sheens. A proper primer seals the surface for even absorption. Bare wood: wood grain, knots, and tannins bleed through latex paint without a shellac or oil-based primer on bare wood. This is especially true for cedar, pine, and redwood. Bare metal: primer prevents rust and adhesion failure. Exterior bare masonry/concrete: specialty masonry primer improves adhesion and reduces porosity. Major color change (especially dark to light): a gray or tinted primer reduces the number of finish coats needed. Stained surfaces (water stains, nicotine, grease): standard primers help but shellac-based primers (Zinsser BIN) or high-hide primers are best for stain blocking. When primer is optional but recommended: repainting same color on a stable surface in good condition: 1–2 coats of quality paint may be sufficient without primer. Good results in years with no primer. Repainting different color, same type of finish: often okay without primer if the existing paint is properly bonded, clean, and the color change isn't extreme. When you can skip primer: you're using a "paint + primer in one" product for a same-color repaint on a smooth, clean surface in good condition. (These products have more base solids, but they are not a true replacement for a separate primer in challenging situations.) The bottom line: primer is cheap insurance. On projects where priming is appropriate, it improves adhesion, seals the surface, provides better coverage with fewer finish coats, and extends the life of the paint job. Budget for primer in challenging painting situations — it saves money by reducing the number of finish coats needed.