Paint Calculator: How Much Paint Do You Need for a Room?
Quick Answer
- *One gallon of paint covers approximately 350–400 square feet per coat on smooth, primed walls.
- *A standard 12×12 room needs about 2 gallons for two coats of paint on the walls.
- *Measure wall area, subtract doors and windows, divide by 400 (or 350 for textured walls), then multiply by number of coats.
- *DIY paint costs run $50–$200 per room; professional painting runs $380–$790 per room on average.
How Much Paint Do I Need? The Short Answer
For a typical interior room, one gallon of paint covers 350–400 square feet per coat. Most rooms need two coats, so you'll divide your total wall area by 350–400 and multiply by 2 to get total gallons needed. Round up to the nearest quart or gallon — running short mid-project means a trip back to the store and a potential color mismatch if the batch is different.
According to the EPA, Americans use approximately 1.57 billion gallons of architectural paint each year, and roughly 10% — 157 million gallons — goes unused. Accurate estimation matters both for your wallet and for the environment.
The Paint Coverage Formula
The basic formula is:
Gallons needed = (Total wall area ÷ Coverage per gallon) × Number of coats
Standard coverage rates by surface type:
- Smooth, primed drywall: 350–400 sq ft per gallon
- Previously painted walls (good condition): 350–400 sq ft per gallon
- Textured or orange-peel walls: 300–350 sq ft per gallon
- Rough brick or concrete: 200–300 sq ft per gallon
- Raw, unpainted drywall: 250–300 sq ft per gallon (high absorption)
When in doubt, use 350 sq ft per gallon as your conservative estimate. You'd rather have a little leftover for touch-ups than run short.
Room Calculation Walkthrough
Here's a step-by-step example for a 12×15 room with 8-foot ceilings:
Step 1: Calculate Total Wall Area
Add up the perimeter of the room, then multiply by ceiling height:
Perimeter = (12 + 15 + 12 + 15) = 54 linear feet
Wall area = 54 × 8 = 432 sq ft
Step 2: Subtract Doors and Windows
Standard deductions:
- Standard door (3×7 ft): ~21 sq ft
- Average window (3×4 ft): ~12 sq ft
For our room with one door and two windows:
Deductions = 21 + (12 × 2) = 45 sq ft
Net wall area = 432 − 45 = 387 sq ft
Step 3: Calculate Gallons
387 sq ft ÷ 350 sq ft per gallon = 1.1 gallons per coat
For two coats: 1.1 × 2 = 2.2 gallons
Buy: 3 quarts or 1 gallon + 1 quart (round up)
Not sure about the math? Our free paint calculator handles all of this automatically.
Paint Finish Types: Which to Use Where
Paint finish affects durability, cleanability, and how light reflects off the wall. The American Coatings Association identifies five main sheen levels used in residential interiors.
| Finish | Sheen Level | Best For | Washability |
|---|---|---|---|
| Flat / Matte | 0–5% | Ceilings, formal dining rooms, low-traffic areas | Low — scuffs easily |
| Eggshell | 10–25% | Living rooms, bedrooms, hallways | Medium — wipes clean |
| Satin | 25–35% | Kids' rooms, family rooms, bathrooms | Good — scrub-resistant |
| Semi-Gloss | 35–70% | Kitchens, bathrooms, trim, doors | Very good — moisture-resistant |
| Gloss | 70–85% | Doors, cabinets, accent trim | Excellent — hard and washable |
Higher sheen levels highlight surface imperfections. If your walls have dings, dents, or uneven texture, stick with eggshell or flat. For high-moisture areas like bathrooms and kitchens, go semi-gloss minimum to resist mildew and allow frequent cleaning.
5 Factors That Affect How Much Paint You Need
The 400 sq ft per gallon rule is a starting point. Several variables can push that number lower — sometimes significantly.
1. Color change (light to dark or dark to light)
Going from white to deep navy or vice versa almost always requires a third coat for full, even coverage. Plan for 3 coats when making dramatic color shifts, or use a tinted primer to reduce the number of finish coats needed.
2. Wall texture
Textured walls — skip-trowel, knockdown, or orange-peel — have more surface area than flat walls. Rough textures can cut your effective coverage by 20–30%, dropping from 400 sq ft per gallon to 280–320 sq ft.
3. Paint quality and formulation
Cheap paints have lower pigment concentration, meaning they cover less per gallon and require more coats to achieve the same opacity. Premium paints from brands like Benjamin Moore and Sherwin-Williams typically achieve better one-coat coverage. According to Consumer Reports, premium interior paints can cover up to 15% more square footage per gallon than budget options.
4. Application method
Rollers apply paint at a more consistent thickness than brushes and cover faster. Sprayers are fastest but have significant overspray waste — typically 20–30% of paint goes airborne and doesn't reach the wall. If spraying, buy 25% more paint than your calculation suggests.
5. Surface porosity
New or unpainted drywall, bare wood, and masonry absorb far more paint than previously painted surfaces. Raw drywall can consume a full primer coat before a finish coat adheres properly. Always prime porous surfaces before painting to normalize absorption and reduce total paint needed.
Cost Estimates: DIY vs Professional Painting
According to NAR remodeling cost data and HomeAdvisor/Angi pricing surveys, interior painting is one of the highest-ROI home improvements. The numbers below reflect 2025–2026 averages across major U.S. metros.
| Scope | DIY Cost | Professional Cost |
|---|---|---|
| Single room (12×12) | $50–$150 | $380–$790 |
| Master bedroom (14×16) | $75–$200 | $500–$1,000 |
| Full interior (2,000 sq ft house) | $400–$900 | $3,000–$8,000 |
| Exterior (2,000 sq ft house) | $500–$1,200 | $3,500–$10,000 |
| Kitchen cabinets (repainting) | $100–$300 | $900–$3,800 |
DIY costs cover paint, primer, roller covers, tape, drop cloths, and brushes. Professionals include labor, prep work (patching holes, sanding, caulking), and cleanup. The labor gap is real — but so is the time investment. A two-person professional crew can complete a full room in 4–6 hours. The same job takes most homeowners an entire weekend.
Angi reports that the average cost to paint a single room professionally in the U.S. sits at $580 as of 2025, up 12% from 2023 due to higher labor costs and material prices.
How Much Paint for Trim, Doors, and Ceilings?
Walls get most of the attention, but trim and ceilings need separate estimates.
Ceilings:Multiply room length × width. A 12×15 room has a 180 sq ft ceiling. One quart handles rooms up to about 175 sq ft in one coat; one gallon covers up to 400 sq ft. Most ceilings only need one coat of flat white ceiling paint.
Trim and baseboards:Measure the linear footage of all trim (baseboards, window casings, door casings, crown molding) and multiply by the width in feet. A typical room has 60–80 linear feet of 4-inch baseboard, which is roughly 20–27 sq ft. One quart of trim paint handles most single-room trim jobs easily.
Doors:A standard 6-panel door has about 20 sq ft of paintable surface. One quart covers 4–5 doors in one coat.
For a complete project estimate including flooring and wall coverings, try our square footage calculator and wallpaper calculator for comparison. If you're also budgeting a floor, the flooring cost calculator can help you estimate total room renovation costs.
Buying Paint: Gallons vs Quarts vs 5-Gallon Buckets
Paint comes in quarts (1 qt = 0.25 gal), gallons (1 gal), and 5-gallon buckets. The cost-per-gallon drops sharply as you buy in bulk:
- Quart: $12–$25 (equivalent to $48–$100/gallon)
- Gallon: $25–$70 depending on brand and quality
- 5-gallon bucket: $100–$200 (equivalent to $20–$40/gallon)
If painting more than 3–4 rooms in the same color, the 5-gallon bucket is almost always the better value. It also eliminates batch variation — the slight color difference that can occur between separate gallons mixed at the store.
For single rooms or small accent projects, buy a gallon and save the rest for touch-ups. Sealed paint stored in a cool, dry space stays usable for up to 10 years (latex) or 15 years (oil-based).
Get an exact paint quantity estimate
Try our free Paint Calculator →Planning a bigger renovation? Try our Square Footage Calculator
Frequently Asked Questions
How much paint do I need for a 12x12 room?
A standard 12×12 room with 8-foot ceilings has roughly 384 square feet of wall area. Subtract about 60 sq ft for a door and two windows, leaving 324 sq ft. One gallon covers 350–400 sq ft, so one gallon handles one coat. For two coats — which most pros recommend — buy two gallons.
How many square feet does a gallon of paint cover?
Most interior latex paints cover 350–400 square feet per gallon per coat on smooth, primed surfaces. Rough or porous surfaces like brick, raw drywall, or textured walls may only yield 250–300 sq ft per gallon because the surface absorbs more paint.
Do I need a primer before painting?
Primer is recommended when painting over new drywall, dark colors, stains, or bare wood. It seals the surface and improves adhesion, which means your finish coat covers more evenly and you may need fewer coats. Many modern paints include primer, but they work best on already-painted surfaces.
How much does it cost to paint a room professionally?
According to HomeAdvisor, professional painters charge $2–$6 per square foot of wall area, or $380–$790 for an average 12×12 room. A full 2,000 sq ft house interior runs $3,000–$8,000 depending on region, number of coats, prep work needed, and paint quality.
What paint finish should I use in a bedroom?
Eggshell or satin finish works best in bedrooms. Flat and matte finishes are more forgiving on imperfect walls but harder to clean. Eggshell has a slight sheen and wipes clean with a damp cloth. Satin offers more durability and is a good choice for kids' rooms where scrubbing is likely.
How do I calculate paint for a ceiling?
For ceiling paint, multiply room length by room width to get square footage. A 12×15 room has a 180 sq ft ceiling, which one gallon covers easily in one coat. Ceilings typically need only one coat of flat white ceiling paint unless covering a dark stain or water damage.