The reason you usually buy too much paint (or worse, too little and have to color-match a second batch) is that paint cans don't cover what the label says. The label says 350 ft² per gallon. Reality says 200–325, depending on what you're painting and how. This guide walks through the actual math, where coverage gets eaten, and what to buy for common room sizes.

The basic formula

Paint is sold by the gallon, and one gallon covers about 350 ft² on a smooth, primed wall in a single coat. Almost no real surface meets all three conditions, so the working formula is:

gallons = (wall area × coats) ÷ coverage per gallon

Example: a 12×14 ft bedroom with 8 ft ceilings, two coats on smooth walls. Wall area = 2 × (12 + 14) × 8 = 416 ft². 416 × 2 coats = 832 ft² to cover. 832 ÷ 350 = 2.4 gallons. Round up to 3 gallons, or buy two 1-gallon cans plus one quart for touch-ups.

The paint calculator does this automatically and lets you toggle smooth vs textured surfaces.

Coverage by surface

The 350 ft² number assumes smooth, primed drywall and one coat with a roller. Real coverage is lower for almost everything else:

  • Smooth painted drywall: 350 ft²/gal
  • Lightly textured drywall (orange peel): 300 ft²/gal
  • Knockdown texture: 275 ft²/gal
  • Popcorn ceiling: 200 ft²/gal (and you should probably remove it instead)
  • Brick or stucco: 175–225 ft²/gal — porous surfaces drink paint
  • Bare drywall (unprimed): 200 ft²/gal — the gypsum sucks paint in. Always prime first.
  • Smooth wood (cabinets, doors): 400 ft²/gal — paint flows easily
  • Bare wood: 200 ft²/gal first coat, 350 ft²/gal subsequent — wood drinks finish too

The right move on bare drywall or wood is to use a primer as the first coat, then your finish paint. Primer is cheaper, designed to seal, and means your finish coats actually cover at the rated rate.

One coat vs two coats

Paint manufacturers love to advertise “one-coat coverage” and it's almost never true at production speed. You'll get one coat to look acceptable in three situations:

  • The new color is the same color or darker than the existing wall
  • You're using a high-quality paint+primer hybrid (Behr Marquee, Sherwin-Williams Emerald)
  • The painter is a slow, careful pro applying paint thick enough to be one-coat

Plan two coats by default. Going from a dark color to a light color or covering anything red, orange, or yellow may need three coats — those pigments are weak and bleed through. White over a previously red wall sometimes needs a tinted primer first to kill the color, then two finish coats over that.

Trim, doors, and ceilings

Trim usually doesn't need a separate calculation — a quart covers the trim in a typical bedroom and runs $20-30. Buy semi-gloss for trim so it's washable and visually distinct from the matte/eggshell on the walls.

Doors take about a quart each for two coats on both sides. Six panels adds material. If you're doing more than three doors, buy a gallon and use it for door + trim + closet interiors at the same time.

Ceilings are easy: ceiling area = length × width. Most ceilings get one coat of dedicated ceiling paint (it's thick, less spatter, flat finish). One gallon covers about 400 ft² of ceiling — coverage is better than walls because there's no edges to cut in.

Paint for common room sizes

Two-coat smooth-wall finish, walls only:

  • 10×10 bathroom (8 ft ceiling): 320 ft² × 2 = 640 ÷ 350 = 2 gallons
  • 12×12 bedroom: 384 ft² × 2 = 768 ÷ 350 = 2.5 gallons → buy 3
  • 12×16 living room: 448 ft² × 2 = 896 ÷ 350 = 2.6 gallons → buy 3
  • 20×30 great room (10 ft ceiling): 1,000 ft² × 2 = 2,000 ÷ 350 = 5.7 gallons → buy 6

For a whole-house repaint, sum all wall areas, multiply by 2 (or 3 for color changes), divide by 350, and add 5–10% for touch-ups, drips, and the inevitable can you spill. A typical 1,800 ft² home interior eats 8–12 gallons.

What paint actually costs in 2026

  • Builder-grade flat (Behr Premium Plus, Valspar Pro): $25–35/gal — fine for ceilings, closets, rentals. Two coats minimum.
  • Mid-grade (Behr Ultra, Sherwin Cashmere): $40–55/gal — washable, low-VOC, good color depth. Two coats.
  • Premium (Behr Marquee, Sherwin Emerald, Benjamin Moore Aura): $60–85/gal — true one-coat in most cases, scrubbable, lifetime warranty. Worth the price on bedrooms and living areas.
  • Primer (PVA or stain-blocking): $20–30/gal

The math on premium paint is usually a wash. Two coats of $30 paint = $60 in material; one coat of $80 paint = $80 in material — slightly more, but you save half the labor time. For DIY where time is free, the cheap two-coat path is fine. For paying a pro, premium one-coat saves you money.

Common mistakes to avoid

  • Mixing leftover paint to save money. Sheen mismatches will show. Pour a half-gallon of flat into a gallon of eggshell and the result is a streaky mess that nothing covers.
  • Skipping primer over a stain or water mark. Latex paint won't seal it — the stain bleeds through every coat. Use stain-blocking primer (KILZ, Zinsser BIN) on the spot first.
  • Buying gallons for a 6×8 closet. A quart covers 100 ft² and costs a third of a gallon. Closets, accent walls, and trim usually don't need a full gallon.
  • Forgetting the box of touch-up paint. Hold back at least a quart in a labeled jar (room name + date + sheen) for the inevitable scuffs and nail-pops over the next 5 years.
  • Painting over wallpaper. The seams telegraph through, the moisture in latex paint sometimes loosens the wallpaper glue, and you've doubled your removal cost when you eventually redo it. Always remove wallpaper first.

Quick FAQ

How much paint for a 12x12 room?2.5–3 gallons for walls only with two coats on smooth surfaces. Add a quart for trim and a gallon of ceiling paint if you're doing the ceiling too.

Can I store leftover paint?Yes — push the lid down tight, store at room temp (not garage in winter), and most latex paint stays usable for 2–5 years. If it has a foul smell or won't mix smooth, it's done.

Do I need to prime before repainting? Only when going from oil-based to latex, painting over bare drywall or wood, or covering stains, water marks, or a glossy surface. Repainting an already-painted wall in a similar color: skip primer.

How much does it cost to paint a room?DIY: $80–150 in paint and supplies for a typical bedroom. Pro: $400–700 for the same room (includes labor, prep, and the contractor's premium paint).

Run the numbers: the paint calculator gives gallons for walls + ceiling with smooth or textured coverage and configurable coats. Pair with the drywall calculator if you're finishing fresh sheets first.