How much paint do I need for a 12x12 room?

A 12x12 room with 8-foot ceilings has about 384 sq ft of wall space. Subtracting 1 door (20 sq ft) and 2 windows (30 sq ft) leaves 334 sq ft of paintable area. At 400 sq ft per gallon, you need about 1 gallon for one coat or 2 gallons for two coats. If your walls are textured, add an extra quart or gallon to account for reduced coverage.

How many square feet does a gallon of paint cover?

A standard gallon of interior latex paint covers approximately 350-400 square feet per coat on smooth, previously painted surfaces. Textured walls reduce coverage to 200-300 sq ft per gallon. Exterior paint on wood siding covers 250-350 sq ft, while porous surfaces like brick or stucco may only yield 150-250 sq ft per gallon. Always check the manufacturer's label for the specific product's coverage rate.

Do I need one coat or two coats of paint?

Two coats are recommended for best results in almost all situations. A single coat rarely provides uniform color, especially when changing colors, covering dark walls, or applying lighter shades. One coat may suffice only for minor touch-ups or when applying the same color over a surface in good condition. Always apply primer first when painting new drywall, bare wood, or making a drastic color change.

Should I subtract doors and windows from the paint area?

Yes, subtracting doors (about 20 sq ft each) and windows (about 15 sq ft each) gives a more accurate estimate. In a typical room with 1 door and 2 windows, this saves about 50 sq ft -- potentially the difference between needing 2 gallons versus 3. Some professional painters skip this step as a built-in safety margin, but for budget-conscious homeowners, the subtraction helps avoid overbuying.

What is the difference between flat, eggshell, satin, and semi-gloss paint?

These refer to the sheen (glossiness) of the dried paint. Flat has no shine and hides wall imperfections but is difficult to clean. Eggshell has a subtle warm glow and is the most popular choice for living spaces. Satin has a soft luster and cleans easily, making it ideal for kitchens, bathrooms, and kids' rooms. Semi-gloss is noticeably shiny, highly washable, and best for trim, doors, and cabinets. Higher sheens are more durable and moisture-resistant but show imperfections more.

How much does it cost to paint a room?

For a typical 12x12 bedroom, DIY materials cost $70-$150 depending on paint quality. Budget paint runs $20-30 per gallon, mid-range is $35-50, and premium brands cost $50-75 per gallon. Add $20-40 for roller covers, brushes, painter's tape, and drop cloths. Hiring a professional painter typically costs $200-800 per room depending on size, number of coats, prep work needed, and geographic location.

Paint Calculator

Quick Answer

One gallon of paint covers roughly 350-400 square feet per coat on smooth interior walls. To estimate how much you need, calculate total wall area (perimeter × ceiling height), subtract doors and windows, then divide by 350 and multiply by the number of coats. Most rooms need two coats for full coverage.

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Calculate how many gallons of paint you need for any room, accounting for doors and windows.

Unit

Room Length

Room Width

Wall Height

Number of Doors

~20 sq ft each (standard)

Number of Windows

~15 sq ft each (standard)

Number of Coats

Gallons Needed

Total Wall Area 0 sq ft Doors + Windows Area 0 sq ft Paintable Area 0 sq ft For 1 Coat 0 gallons For 2 Coats 0 gallons

How Paint Calculation Works

A paint calculator is a tool that estimates the number of gallons of paint needed for a room based on wall dimensions, doors, windows, and number of coats. According to the Paint Quality Institute, the average American household uses approximately 8 gallons of paint per year. Estimating the right amount of paint prevents costly return trips to the store and reduces waste. The process involves three steps: calculating the total wall area of the room, subtracting non-paintable surfaces like doors and windows, and dividing the remaining paintable area by the paint's coverage rate. This calculator automates all three steps and rounds up to whole gallons, since paint is sold in full gallon and quart containers.

The total wall area is calculated from the room perimeter -- two times the length plus two times the width -- multiplied by the wall height. This gives you the square footage of all four walls combined. Doors and windows are then subtracted because you do not paint those surfaces. A standard interior door occupies about 20 square feet (roughly 3 feet wide by 6 feet 8 inches tall), and a standard window occupies about 15 square feet (roughly 3 feet wide by 5 feet tall).

Once you have the net paintable area, divide it by the paint's coverage rate (typically 350-400 square feet per gallon for smooth surfaces) and multiply by the number of coats. Two coats are standard for most painting projects because a single coat rarely provides uniform color and coverage, especially when painting over a different color or new drywall.

Paint Formula

Gallons Needed

Gallons = (Total Wall Area − Openings) × Coats ÷ Coverage Rate

Total Wall Area

Wall Area = 2 × (Length + Width) × Height

Openings

Openings = (Doors × 20 sq ft) + (Windows × 15 sq ft)

Worked example: A bedroom is 14 feet long, 12 feet wide, and 8 feet high with 1 door and 2 windows. Wall area = 2 × (14 + 12) × 8 = 416 sq ft. Openings = (1 × 20) + (2 × 15) = 50 sq ft. Paintable area = 416 − 50 = 366 sq ft. For 2 coats at 400 sq ft per gallon: 366 × 2 ÷ 400 = 1.83 gallons, rounded up to 2 gallons.

Key Terms

Term	Definition
Coverage Rate	The number of square feet one gallon of paint can cover in a single coat. Typically 350-400 sq ft for latex on smooth surfaces.
Primer	A preparatory coating applied before paint to improve adhesion, block stains, and create a uniform base. Essential on new drywall, bare wood, and drastic color changes.
Coats	The number of layers of paint applied. Two coats are standard for even coverage and color consistency.
Sheen	The level of glossiness in the dried paint finish, ranging from flat (no shine) to high gloss (maximum shine). Higher sheens are more washable but show more imperfections.
VOC	Volatile Organic Compounds -- chemicals that evaporate from paint as it dries, contributing to odor and air quality concerns. Low-VOC and zero-VOC paints are available for healthier indoor air.
Mil Thickness	Paint film thickness measured in thousandths of an inch. A typical coat of latex paint dries to 1.0-1.5 mils. Two coats give 2-3 mils of dry film thickness.
Drying Time	The time between coats. Latex paint is typically dry to the touch in 1-2 hours and ready for a second coat in 2-4 hours. Oil-based paint requires 6-8 hours between coats.

Paint Coverage by Type

Different paint sheens have slightly different coverage rates and are suited for different rooms and surfaces. Higher-sheen paints tend to spread more easily and cover slightly more area per gallon, but they also highlight surface imperfections more visibly.

Sheen	Coverage per Gallon	Best For	Washability
Flat / Matte	350-400 sq ft	Ceilings, low-traffic rooms, walls with imperfections	Low -- scuffs easily
Eggshell	350-400 sq ft	Living rooms, bedrooms, dining rooms	Moderate
Satin	350-400 sq ft	Kitchens, bathrooms, hallways, kids' rooms	Good -- wipes clean easily
Semi-Gloss	350-400 sq ft	Trim, doors, cabinets, bathrooms	Very good -- resists moisture
High Gloss	400-450 sq ft	Trim, doors, furniture, accent surfaces	Excellent -- most durable

Practical Examples

Single bedroom (12 x 12 x 8 ft): Perimeter = 2 × (12 + 12) = 48 ft. Wall area = 48 × 8 = 384 sq ft. Subtract 1 door (20 sq ft) and 2 windows (30 sq ft) = 334 sq ft paintable. For 2 coats: 334 × 2 ÷ 400 = 1.67, round up to 2 gallons. At $35-50 per gallon for mid-range paint, budget $70-100 for paint plus $20-30 for supplies (roller, tray, tape, drop cloth).

Entire house interior (1,800 sq ft home): A typical 1,800 sq ft home has roughly 4,500-5,500 sq ft of paintable wall space after subtracting doors and windows. For 2 coats at 400 sq ft per gallon: approximately 23-28 gallons for walls. Add 2-3 gallons for ceilings (if painting those too) and 1-2 gallons of semi-gloss for trim. Total: 26-33 gallons. At $40 per gallon, materials run $1,040-$1,320. Professional painters typically charge $3,000-$6,000 for a whole-house interior.

Exterior painting (2-story home): A 2,000 sq ft two-story home might have 2,500-3,500 sq ft of exterior wall surface after subtracting windows and doors. Exterior paint coverage varies more due to surface texture -- expect 250-350 sq ft per gallon on wood siding, less on stucco or brick. For 2 coats: approximately 15-28 gallons depending on surface. Exterior paint costs $35-60 per gallon, and professional exterior painting runs $4,000-$10,000 for a full house.

Tips for Estimating Paint

Always round up. Paint is sold in gallons and quarts. If your calculation comes to 2.1 gallons, buy 3 gallons or 2 gallons plus 1 quart. The leftover paint is valuable for future touch-ups -- store it sealed in a climate-controlled space, and it will last for years.

Primer matters. New drywall, bare wood, repaired patches, and drastic color changes all require primer. Primer is cheaper than paint ($15-25 per gallon) and improves adhesion, blocks stains, and reduces the number of topcoats needed. Self-priming paints exist but perform best over previously painted surfaces in good condition, not on raw or stained surfaces.

Ceiling paint is different. Ceiling paint is formulated to be thicker (less drip) and typically comes in flat white only. Ceilings usually need only 1 coat unless they are stained or you are making a significant color change. Calculate ceiling paint separately from wall paint: length × width ÷ 400 = gallons for one coat.

Textured surfaces need more paint. Knockdown, orange peel, popcorn, and other wall textures increase surface area by 20-50%, reducing effective coverage to 200-300 sq ft per gallon. If your walls are textured, reduce the coverage rate in your estimate or simply plan to buy 25-50% more paint than the smooth-surface calculation suggests.

Buy all paint at once. Paint colors can vary slightly between batches. Purchase all your paint at once from the same store, and ask them to shake the cans on the same day. For large projects, "box" your paint by mixing multiple gallons together in a 5-gallon bucket to ensure perfectly uniform color across all walls.

This calculator is for informational purposes only and does not constitute financial, tax, or legal advice. Always consult a qualified professional for decisions specific to your situation.