Paint Calculator — Walls, Ceilings & Exteriors

Calculator

Room perimeter

Wall height

Length

Width

Number of doors

≈ 20 sq ft each

Number of windows

≈ 15 sq ft each

Number of coats

Paint coverage

Price per gallon (optional)

$/gal

Paint needed

2 gallons

Paintable area: 366 sq ft · With 2 coats: 732 sq ft of coverage

Estimated paint cost: $90 paint only, excludes primer, supplies, labor

How to Calculate Paint Needed

Paint coverage is straightforward once you have the right numbers: surface area, number of coats, and coverage rate. The most common DIY mistake isn't math — it's forgetting that ceiling paint and wall paint are usually different products, and that primer covers less than finish paint per gallon.

Wall area = Room perimeter × wall height
Paintable area = Wall area − (doors × 20) − (windows × 15)
Gallons = (Paintable area × coats) ÷ coverage per gallon

Standard interior latex covers 350-400 sq ft per gallon on smooth surfaces. Drop to 300 for lightly textured walls, 250 for stucco or popcorn ceilings, and 200 for raw drywall, masonry, or anywhere primer is still curing. Buy paint by the gallon — sometimes one-gallon and one-quart combinations save money on small jobs.

Worked example: bedroom repaint

A 12 × 14 ft bedroom with 8 ft ceilings, one door, two windows, going from beige to soft blue:

Perimeter: (12 + 14) × 2 = 52 ft
Wall area: 52 × 8 = 416 sq ft
Less openings: 416 − 20 (door) − 30 (2 windows × 15) = 366 sq ft
With 2 coats: 366 × 2 = 732 sq ft to cover
Gallons at 350 sq ft/gal: 732 ÷ 350 = 2.1 gallons — buy 2.5 gallons (round up)
Plus ceiling paint: 12 × 14 = 168 sq ft × 1 coat ÷ 350 = ~0.5 gallon (one quart)
Total paint cost (at $45/gal): $135 (walls) + $15 (ceiling) = $150

Buy 10-15% extra, but don't open the spare

Keep an unopened can of the same batch as your touch-up paint. Wall paint that's been opened and partially used dries differently than fresh paint, even when applied to the same wall. Store the touch-up can in a closet, label it with the room and date.

Paint Coverage by Surface Type

Manufacturers print 400 sq ft/gallon on the can, but real-world coverage varies dramatically with surface texture, color change, and application method. Plan with these realistic figures.

Surface	Coverage per gallon	Coats needed	Notes
Smooth painted drywall	400 sq ft	2	Best-case scenario
Lightly textured wall	350 sq ft	2	Most repaints
Knockdown / orange peel	300 sq ft	2	Standard new build
Heavy texture / popcorn	250 sq ft	2	Use thick-nap roller
Bare drywall (no primer)	200 sq ft	3	Prime first, save paint
Bare wood (primer included)	250 sq ft	2-3	End grain absorbs more
Stucco / brick	200 sq ft	2	Use masonry paint
Metal (with primer)	400 sq ft	2	Use direct-to-metal paint
Smooth doors / cabinets	350 sq ft	2	Use thin-nap roller or sprayer

Paint Types and When to Use Each

Interior latex (water-based)

Standard for walls, ceilings, and trim in most modern homes. Easy cleanup with water, low odor, dries in 1-4 hours. Cost: $25-50/gallon for builder grade, $50-80 for premium. Brands like Behr, Sherwin-Williams Emerald, Benjamin Moore Regal Select, Valspar Reserve are top-rated.

Interior oil-based (alkyd)

Hard, durable finish for trim, doors, and cabinets. Longer dry time (6-8 hours) but yields a glass-smooth finish. Strong odor, mineral-spirits cleanup, slow yellowing over years. Increasingly rare due to VOC restrictions in many states. Cost: $40-70/gallon.

Exterior paint

Formulated for UV, moisture, and temperature swings. Acrylic latex is the dominant choice — flexible, breathable, holds color. Apply when air temperature is 50-85°F and no rain expected within 24 hours. Cost: $40-80/gallon. Two coats is mandatory for warranty validity on most premium brands.

Primer

Use for bare surfaces, stains, and major color changes. Latex primer is standard. Stain-blocking primers (Kilz, BIN, Zinsser) for water stains, smoke, and knots in wood. Bonding primer for slick surfaces like laminate or tile. Coverage: 200-300 sq ft/gal. Cost: $20-40/gallon.

Specialty paints

Kitchen and bath (mildew-resistant), high-traffic (scuff-resistant), chalkboard, magnetic, ceiling flat, masonry, swimming pool, garage floor epoxy. Each has specific coverage and prep requirements — always check the can.

Paint Cost Breakdown 2026

Category	Per gallon	Per sq ft (2 coats)	Notes
Builder grade interior	$25-35	$0.15-0.20	Behr Premium Plus, Valspar 2000
Mid-grade interior	$40-55	$0.25-0.30	Behr Ultra, BM Regal, SW SuperPaint
Premium interior	$60-90	$0.35-0.50	BM Aura, SW Emerald, Farrow & Ball
Designer / boutique	$100-180	$0.55-1.00	Farrow & Ball, Backdrop, Portola
Exterior latex	$45-85	$0.30-0.50	Holds up to weather 10-15 yrs
Primer	$20-45	$0.15-0.25	One coat under finish

Professional labor adds $1.50-3.50 per sq ft of wall area for interior, $2-5 for exterior including prep, materials, and cleanup. A 12 × 14 bedroom costs $300-700 to have painted professionally, depending on prep needed and ceiling height. DIY material cost for the same room: $80-150.

Prep Work: 80% of a Good Paint Job

Paint is only as good as the surface underneath it. Skipping prep is the #1 reason DIY paint jobs look bad or fail within a year.

Clean the surface. Walls: mild detergent and water. Kitchen and bath: degrease with TSP substitute. Exterior: pressure wash or scrub with deck cleaner.
Repair imperfections. Fill nail holes with spackle, sand smooth. Patch larger holes with mesh and joint compound. Caulk gaps where wall meets trim, ceiling, and adjacent rooms.
Sand glossy surfaces. Trim, doors, and cabinets need light sanding (220 grit) to give the new paint something to bite into.
Mask edges. Painter's tape (Frog Tape or 3M Blue) along baseboards, ceiling line, and adjacent walls. Press the edge firmly to prevent bleed-through.
Drop cloths. Canvas for floors (reusable, breathable), plastic for furniture (cheap, traps splatter).
Prime as needed. Bare drywall, stains, dark-to-light changes. Tinted primer for dark colors saves a coat.
Cut in first. Use a 2.5-inch angled brush around edges, then roll the field. Working in 3-4 ft sections keeps the wet edge moving.

Paint Sheens: Where to Use Each

Sheen	Where to use	Pros	Cons
Flat / matte	Ceilings, low-traffic walls	Hides imperfections; non-reflective	Marks easily; hard to clean
Eggshell	Living rooms, bedrooms, halls	Subtle sheen; wipes clean	Shows lap marks if not careful
Satin	Kids' rooms, hallways, bathrooms	Scrubbable; mild sheen	Shows imperfections more
Semi-gloss	Trim, doors, bathrooms, kitchens	Durable; very washable	Highlights every flaw
Gloss / high-gloss	Cabinets, accent doors, furniture	Hardest finish; glass-smooth	Shows every dust speck

How Long Does Paint Last?

Modern paint quality is excellent — repaints are driven more by color preference than failure. Realistic intervals between repaints:

Living room, bedroom walls: 5-10 years (mostly aesthetic)
Kitchen walls and ceiling: 3-5 years (grease, steam)
Bathroom: 3-5 years (moisture, mildew)
Hallways, stairwells: 2-4 years (high traffic, scuff marks)
Trim and doors: 5-8 years
Exterior body: 7-15 years (climate-dependent)
Exterior trim: 4-8 years (south- and west-facing fade first)

Common Paint Mistakes

Buying too little paint: Running out mid-wall and changing batches creates visible color streaks. Buy 10-15% extra; you can return unopened.
Skipping primer: Bare drywall, stains, or major color changes need primer. "Paint and primer in one" is a marketing claim, not always a substitute.
Painting in extreme conditions: Below 50°F or above 85°F causes flash drying or poor adhesion. Avoid direct sun on exterior surfaces.
Cheap brushes and rollers: A $25 brush lasts 10 years and lays paint better than a $5 brush. Same for roller covers — buy quality, save effort.
Not boxing paint cans: Mix all gallons of the same color in a 5-gallon bucket before starting. Eliminates batch-to-batch color variation.
Rushing the second coat: Wait 4 hours minimum for latex; second coat applied too soon lifts the first.
Painting over dirty walls: New paint won't adhere to grease, dust, or smoke. Always clean first.
Forgetting to stir: Pigment settles in the can. Stir for 2 minutes when you open, and every 30 minutes during use.

Frequently Asked Questions

How much paint do I need for a 12x14 room?

For a 12 by 14 room with 8 ft ceilings: walls are (12+14) × 2 × 8 = 416 sq ft. Subtract one door (20 sq ft) and two windows (15 sq ft each) = 366 sq ft paintable. With 2 coats at 350 sq ft/gal coverage: 366 × 2 ÷ 350 = 2.1 gallons. Round up to 2.5 gallons or one gallon plus one quart.

How much area does one gallon of paint cover?

Standard interior latex paint covers 350-400 sq ft per gallon on smooth walls in a single coat. Textured walls drop to 250-300 sq ft per gallon. Bare drywall or fresh masonry absorbs more, dropping coverage to 200-250 sq ft per gallon. Always check the can label — premium paints can cover 450 sq ft.

How many coats of paint do I need?

Two coats is the standard for most residential repainting — first coat lays down color, second coat evens out coverage. One coat works for refreshing the same color over recently painted walls. Three coats are needed for light over dark, dark over white, or coverage over patchwork repairs.

Do I need primer?

Yes, for: bare drywall, raw wood, dark-to-light color changes, repaired patches, glossy surfaces, water stains, and high-moisture areas. Skip primer when: recoating same color, modern paint-and-primer-in-one products are being used, and surface is clean. Primer typically covers 200-300 sq ft per gallon.

How do I calculate paint for an exterior?

Measure perimeter of house × wall height for total wall area. Subtract windows and doors. Add 5-10% for waste, soffits, and trim. A typical 2,000 sq ft house has about 2,400 sq ft of exterior wall — needs 7-8 gallons for two coats. Exterior paint coverage runs 300-400 sq ft per gallon depending on surface texture.

How much paint for a ceiling?

Ceiling area = room length × room width. A 12 × 14 room has 168 sq ft of ceiling. With flat ceiling paint (typical 350 sq ft/gal) at 2 coats: 168 × 2 ÷ 350 = 0.96 gallon. Round up to one gallon. Ceilings only need one coat if you're refreshing the same white.

How much does it cost to paint a room?

DIY: $50-150 in paint and supplies for an average bedroom. Professional: $300-700 per room, varying by region, prep work, and ceiling height. The paint itself ($80-150) is usually 20-30% of the total professional cost — the rest is labor, prep, and supplies.

What's the difference between flat, eggshell, and satin paint?

Flat hides imperfections but marks easily — best for ceilings and low-traffic walls. Eggshell has subtle sheen and wipes clean — most popular for living areas. Satin is slightly shinier and more durable — great for hallways and kids' rooms. Semi-gloss for trim and bathrooms. Gloss for doors and cabinets.

How much paint per square foot?

1 gallon ÷ 350 sq ft coverage = roughly 1 gallon per 175 sq ft for 2 coats, or about $0.13 per sq ft in paint alone at $45/gallon. Add primer ($0.05-0.08/sq ft) and supplies for total DIY material cost around $0.20-0.30 per sq ft of wall.

Can I mix gallons of paint to get the same color?

Yes — and it's strongly recommended. Open all cans of the same color, pour them together into a 5-gallon bucket, and stir thoroughly. This is called 'boxing' the paint. Different cans can have subtle batch variations; mixing them eliminates color streaks at can-changeover points on the wall.

How long does paint take to dry?

Latex paint is dry to the touch in 1 hour, recoatable in 4 hours, fully cured in 30 days. Don't apply the second coat too early — it can lift the first. Don't wash freshly painted walls for 30 days; the paint film is still hardening. Oil-based paints take longer: 6-8 hours recoat time, 7 days cure.

How do I store leftover paint?

Wipe rim clean, hammer lid tight, store upside down in a cool place. Inverting creates an airtight seal at the bottom (now top). Properly stored latex paint lasts 5-10 years. Discard if it smells sour, has a thick skin throughout the can, or won't blend when stirred.