Paint Estimator

How This Calculator Works

Paint is one of the highest-ROI cosmetic upgrades a homeowner can do — and one of the most commonly mis-estimated. The math itself is dead simple, but the inputs hide nuance: door and window areas to subtract, coats required for color changes, coverage variation between brands, and labor costs that swing 3-5× depending on whether you DIY or hire a painter.

The core formula:

Walls = 2 × (length + width) × ceiling height − (doors × 21) − (windows × 15)

Gallons = (paintable area × coats) ÷ coverage per gallon → rounded up

Standard interior latex paint covers 350–400 sqft per gallon on smooth drywall with a roller. Heavy texture (knockdown, popcorn ceiling, masonry) cuts that to 200–250 sqft. The default coverage of 350 sqft assumes typical drywall walls — if you're painting brick or textured ceilings, drop coverage to 250–275.

Always 2 coats. The exception is a color-on-color same-brand repaint with a fresh wall — then 1 coat is fine. New construction, color changes (especially light over dark), and any wall that's been patched all require 2 coats. The calculator defaults to 2 because that's the realistic scenario.

Ceiling and trim. If you toggle Include ceiling, the calculator adds length × width to the paintable area. Ceiling paint is its own product (flat finish, no sheen) and typically costs the same as wall paint. Trim (baseboards, doors, window frames, crown molding) adds roughly 20% to wall surface area but requires a different paint (semi-gloss enamel) and significantly more time to cut in cleanly.

Understanding Your Results

Four outputs to read in order:

• Gallons needed — the headline. Round up; a leftover quarter-gallon for touch-ups is worth more than running out mid-coat. For rooms over 400 sqft of paintable area, calculate 2 coats and buy 1 extra gallon for touch-ups.
• Paintable area (sqft) — the bottom line surface to paint, after deducting doors and windows. A standard 12×14 bedroom with 8-foot ceilings, 2 doors, and 2 windows yields about 320 sqft of paintable wall.
• Paint cost vs Labor cost — paint is usually 25-40% of total project cost when you hire. Labor at $3.50/sqft on 320 sqft adds $1,120; paint alone is ~$80 for 2 gallons. DIY essentially eliminates the labor cost.
• Total — paint + labor + 10% supplies (tape, drop cloths, brushes, rollers, primer if needed). Use this to vet contractor quotes — if their bid is 50%+ above this number, ask what's different.

The surface breakdown table tells you where the area comes from: walls vs ceiling vs trim. If trim is included, you'll notice it adds ~60 sqft to a typical bedroom — which usually requires a separate quart of semi-gloss enamel beyond your wall gallons.

Gallon-vs-quart purchasing. Paint is sold by the gallon, half-gallon, and quart. Per-quart pricing is roughly 30% higher per unit, so always size up to gallons when you're over ~1.5 quarts. Leftover paint stores well for 2+ years if the can is sealed properly.

Factors That Affect Paint Quantity

Color change (dark to light)

Going from a dark color (navy, charcoal, hunter green) to a light color (white, pale gray) typically requires 3 coats unless you use a tinted primer. Each coat adds ~30 sqft/gallon of effective consumption. For these conversions, set coats to 3 or budget an extra gallon of primer.

Wall texture and porosity

Smooth-rolled drywall: 350-400 sqft/gallon. Lightly textured (orange peel): 300-350. Heavy texture (knockdown, popcorn): 200-275. Brick, concrete block, stucco: 150-200. New unprimed drywall is highly porous and consumes the first coat as primer — 50% more than the spec'd coverage.

Paint quality tier

Builder-grade paint ($20-25/gallon) covers worse, often requires 3 coats, and lasts 3-5 years. Mid-tier ($35-45/gallon, Behr Marquee, Sherwin Williams SuperPaint) typically covers in 2 coats and lasts 7-10 years. Premium ($55-80/gallon, Aura, Emerald) often covers in 1-2 coats and lasts 12-15 years. Per-square-foot lifetime cost is usually lowest with mid-tier or premium.

Primer requirements

Skip primer only if: existing paint is the same color family, walls are in good condition, and the new paint is self-priming. Always prime when: switching dramatically colors, painting over stains, covering patched drywall, or painting raw drywall or wood. Primer is ~$25/gallon and covers 200-300 sqft.

Sprayer vs roller vs brush

HVLP sprayers cover 25-30% faster than rolling but waste 30-40% of paint to overspray and require extensive masking. For interior residential work, roller + brush is usually the right call. Sprayers shine for exterior, cabinets, fences, and ceilings with no fixtures.

Trim work

Trim isn't included in the wall area unless you toggle it. A typical room has 50-80 linear feet of baseboard plus door and window casings — about 60-80 sqft of trim surface. Trim paint requires a separate semi-gloss enamel and cuts in painstakingly to avoid bleed onto the walls.

Hiring a painter vs DIY

Pro painters charge $2-5/sqft for walls only ($30-90/sqft for cabinets and trim). On a 320 sqft room, that's $640-1,600 in labor. DIY a room saves $500-1,500 but takes a typical homeowner 8-15 hours per room including taping and cleanup. The break-even hourly rate is ~$50/hr.

Special conditions

Mildew or smoke damage requires a stain-blocking primer ($35-50/gallon) before topcoat. Lead paint in pre-1978 homes requires EPA RRP-certified handling for any disturbance. Bathrooms and kitchens benefit from mildew-resistant paint (Aura Bath & Spa or equivalent) which costs 20-30% more but lasts in humid environments.

Frequently Asked Questions

Next Steps

Once you have the gallon and cost estimates, the natural next steps:

• Flooring Cost Calculator — paint + new flooring is the classic refresh combo.
• Renovation ROI Calculator — paint recoups 60-100% of cost at sale; check the broader project list.
• Deck Cost Calculator — if you're going outside, model the deck refinish/rebuild.
• DIY vs Pro Costs — painting is one of the highest-DIY-savings categories.
• Home Maintenance Schedule — when to repaint interior vs exterior.