How Much Paint Do You Need for a Room? Complete Guide

Running out of paint mid-project means a trip to the store and risking a color mismatch if they’re out of your batch. Buying too much means wasted money and disposal hassles. This guide shows you exactly how much paint you need.

The Quick Answer

For a 12×12 foot room with 8-foot ceilings and two coats:

• Wall area: 384 sq ft
• Paint needed: 1.5 gallons
• Cost estimate: $45–$90 (at $30–$60 per gallon)

For a 10×10 room: 1 gallon (two coats).

For a 15×15 room: 2 gallons (two coats).

The Formula

Paint quantity comes down to wall area divided by coverage rate:

Gallons Needed = Wall Area ÷ Coverage Rate × Number of Coats

Step-by-Step Calculation

1. Calculate wall area: Multiply perimeter times height, where perimeter equals two times length plus two times width
2. Subtract openings: Deduct door area of 21 sq ft and window area of 15 sq ft each
3. Divide by coverage: Most paints cover 350 to 400 sq ft per gallon
4. Multiply by coats: Usually 2 coats for color changes, 1 for touch-ups

Example: 12×12 Room with 8-Foot Ceilings

1. Perimeter equals 2 times 12 plus 2 times 12, which is 48 feet
2. Wall area equals 48 times 8, which is 384 sq ft
3. Subtract door of 21 sq ft and one window of 15 sq ft to get 348 sq ft
4. Paint per coat = 348 ÷ 350 = 1 gallon
5. Two coats = 2 gallons total

Round down to 1.5 gallons if the room is empty with no furniture masking and you’re an experienced painter. Otherwise, buy the full 2 gallons.

Room Size Reference Chart

Room Size	Ceiling Height	Wall Area	1 Coat	2 Coats
Small 8×10	8 ft	288 sq ft	0.75 gal	1.5 gal
Bedroom 10×12	8 ft	352 sq ft	1 gal	2 gal
Standard 12×12	8 ft	384 sq ft	1 gal	2 gal
Large 12×15	8 ft	432 sq ft	1.25 gal	2.5 gal
Master 15×18	8 ft	528 sq ft	1.5 gal	3 gal
Living Room 18×20	9 ft	684 sq ft	2 gal	4 gal

Assumes one door and two windows. Coverage at 350 sq ft/gallon.

One Coat vs Two Coats

When One Coat Works

• Same color touch-up
• Light color over light color (beige to off-white)
• High-quality paint with primer built in
• Previously painted walls in good condition

Coverage: 350–400 sq ft per gallon

When Two Coats Are Required

• Any color change (especially dark to light)
• First time painting new drywall
• Covering stains or marks
• Transitioning from flat to glossy finish
• Builder-grade paint needing upgrade

Coverage: 175–200 sq ft per gallon (total for both coats)

Professional painters default to two coats. The first coat seals and levels, while the second coat provides uniform color and durability. Skipping the second coat leads to uneven color, visible roller marks, and premature wear.

Paint Finish Types

Paint finish affects both coverage and durability. The same gallon covers different square footage based on sheen.

Flat/Matte (400 sq ft/gallon)

Best coverage due to higher pigment ratio and no reflective particles.

Pros:

• Hides wall imperfections
• Easy touch-ups (no sheen variation)
• Deep, rich color

Cons:

• Not washable, so marks are permanent
• Shows traffic wear quickly

Best for: Ceilings, low-traffic bedrooms, and formal dining rooms

Eggshell (375 sq ft/gallon)

Slight sheen, better washability than flat.

Pros:

• Hides minor imperfections
• Wipeable with gentle cleaning
• Most popular for living spaces

Cons:

• Touch-ups can show sheen differences
• Not as durable as satin

Best for: Living rooms, dining rooms, hallways

Satin (350 sq ft/gallon)

Soft sheen, good durability.

Pros:

• Fully washable because you can scrub marks off
• Resists moisture and mildew
• Smooth, silky appearance

Cons:

• Shows wall flaws more than flat
• Requires better prep work

Best for: Kitchens, bathrooms, kids’ rooms, trim

Semi-Gloss (325 sq ft/gallon)

Noticeable shine, high durability.

Pros:

• Extremely washable, so you can scrub with cleaner
• Moisture-resistant
• Reflects light and brightens rooms

Cons:

• Highlights every wall imperfection
• Requires perfect prep like skim coating walls

Best for: Bathrooms, trim, doors, cabinets

High-Gloss (300 sq ft/gallon)

Lowest coverage due to high resin content.

Pros:

• Ultra-durable with furniture-grade finish
• Easiest to clean
• Mirror-like finish

Cons:

• Shows every flaw
• Requires professional-level prep

Best for: Cabinets, furniture, front doors

Key takeaway: Higher sheen means less coverage, so budget an extra quart if switching from flat to semi-gloss.

Coverage by Surface Type

The substrate you’re painting dramatically affects coverage.

New Drywall (250 sq ft/gallon)

Bare drywall is porous and absorbs paint like a sponge.

Requirements:

• Prime first using PVA primer, which is recommended
• Plan for 3 coats total: 1 primer plus 2 paint
• Coverage with primer: 300 sq ft/gallon
• Coverage without primer: 250 sq ft/gallon

Skipping primer on new drywall wastes paint. The first coat disappears into the wall, and you’ll need 3 to 4 paint coats to match the coverage of 1 primer plus 2 paint.

Previously Painted Walls (375 sq ft/gallon)

Standard coverage if the existing paint is in good condition.

Best case: Same color family, no damage, low sheen to low sheen.

Reduce coverage if:

• Switching from dark to light because you’ll need extra coats
• Old paint is glossy, so sand first for adhesion
• Wall has repairs where spackle patches absorb more paint

Textured Walls (250–300 sq ft/gallon)

Orange peel, knockdown, and popcorn textures have more surface area than flat walls do.

Coverage factors:

• Light texture like orange peel: 325 sq ft/gallon
• Medium texture like knockdown: 300 sq ft/gallon
• Heavy texture like skip trowel: 250 sq ft/gallon

Use a thick nap roller measuring 3/4 inch to 1 inch to get into texture valleys. Standard 3/8 inch nap rollers leave unpainted gaps.

Bare Wood (200 sq ft/gallon)

Unpainted wood is extremely porous.

Requirements:

• Prime first using oil-based primer for tannin bleed prevention
• Sand between coats with 120-grit sandpaper
• Plan for 1 primer plus 2 to 3 paint coats

Wood grain absorbs paint unevenly. Knotty pine needs extra coats over knots to prevent bleed-through.

Masonry/Concrete (150 sq ft/gallon)

Most porous surface. Some paints list concrete coverage separately on the can.

Requirements:

• Use masonry primer that blocks efflorescence
• Use masonry paint or elastomeric coating
• Plan for 1 primer plus 2 paint coats minimum

Concrete block is worse than poured concrete due to exposed aggregate. Budget double the paint for block walls.

Pro Tips from Professional Painters

1. Buy by the Gallon, Not the Quart

A gallon costs $30 to $60, while four quarts cost $12 each, which equals $48.

Even if your calculation says “1.2 gallons,” buy 2 gallons instead of 1 gallon plus 1 quart because you’ll pay less per ounce, and leftovers are useful for touch-ups.

2. The 10% Rule

Add 10% to your calculated amount to account for:

• Spillage and tray waste
• Touch-ups during installation when you hit the ceiling or drips occur
• Future repairs, so store leftover paint for 2 to 3 years

If math says 1.5 gallons, buy 2 gallons. The extra half-gallon isn’t waste, it’s insurance.

3. Don’t Subtract Doors and Windows for Small Rooms

In rooms under 150 sq ft, skip the subtraction step for these reasons:

• Painting around trim wastes paint because cutting in uses more than rolling
• The math difference is small, with one door saving only 0.06 gallons
• You’ll use that paint for extra coats on repairs or texture

For large rooms over 300 sq ft, subtract openings to avoid buying an unnecessary gallon.

4. Different Batches = Different Colors

Paint color varies between batches even in the same formula. The batch code is on the can.

Correct: Buy all paint for a room or connected rooms at once. If you need 3.5 gallons, buy 4 gallons from the same batch.

Wrong: Buy 2 gallons, use them, then buy 2 more next week because the second batch will look different under natural light.

5. Ceilings Use Less Paint Than You Think

Ceilings are flat surfaces with no cut-ins or obstacles.

Coverage: 400 sq ft/gallon (best-case scenario)

For a 12×12 room:

• Ceiling area = 144 sq ft
• Paint needed = 144 ÷ 400 = 0.36 gallons (one coat)

One gallon covers two coats on a 200 sq ft ceiling. Don’t overbuy ceiling paint because it doesn’t get wear and rarely needs touch-ups later.

6. Quality Paint Costs Less in the Long Run

Budget paint at $20 to $30 per gallon:

• Coverage: 250 to 300 sq ft/gallon
• Coats needed: 3 or more
• Durability: 2 to 3 years before repainting

Premium paint at $50 to $70 per gallon:

• Coverage: 375 to 400 sq ft/gallon
• Coats needed: 2
• Durability: 7 to 10 years before repainting

For a 12×12 room:

• Budget: 3 coats times 2 gallons equals $120 plus labor for third coat
• Premium: 2 coats times 1.5 gallons equals $105

Premium paint covers better, hides flaws, and lasts longer. You’ll save money even before factoring in reduced labor.

Common Paint Estimation Mistakes

1. Forgetting the Second Coat

Scenario: You calculate 350 sq ft of wall area, buy one gallon, and paint the room. The color looks thin and uneven.

Reality: You needed two coats because one gallon covers 350 sq ft once, but you needed 700 sq ft of coverage, which equals 350 sq ft times 2 coats.

Fix: Multiply your wall area by the number of coats before dividing by coverage rate.

2. Using Ceiling Height Instead of Wall Height

Wrong: “My ceiling is 8 feet, so wall height is 8 feet.”

Right: Wall height is floor to ceiling minus baseboards and crown molding.

If you have 6-inch baseboards and 4-inch crown molding, your paintable wall height is:

• 8 feet equals 96 inches
• Minus 6 inch baseboard equals 90 inches
• Minus 4 inch crown equals 86 inches
• Paintable height equals 7.2 feet

That’s a 10% reduction in paint needed. Measure the actual paintable wall, not the architectural ceiling height.

3. Ignoring Doors and Windows in Large Rooms

Scenario: You’re painting a 20×25 living room with 9-foot ceilings, 3 windows, and 2 doors.

Area without subtraction: 810 sq ft Area with subtraction: 810 minus 42 for doors minus 45 for windows equals 723 sq ft

That’s 87 sq ft saved, which equals 0.25 gallons. In a large room, subtracting openings matters.

4. Assuming All Paints Cover the Same

Scenario: You switch from Behr to Sherwin-Williams mid-project and wonder why coverage differs.

Reality: Coverage varies by brand and quality:

• Budget brands: 250 to 300 sq ft/gallon
• Mid-tier brands like Behr and Valspar: 350 to 375 sq ft/gallon
• Premium brands like Sherwin-Williams and Benjamin Moore: 375 to 400 sq ft/gallon

Check the coverage rate on the can before calculating. Don’t assume 350 sq ft/gallon.

5. Not Accounting for Color Changes

Light to Dark: Usually fine with 2 coats.

Dark to Light: Requires 2 to 3 coats because dark base paint bleeds through light topcoats.

If you’re going from navy blue to white:

• Prime with tinted primer like gray primer for white topcoat
• Plan for 1 primer plus 2 to 3 paint coats
• Triple your paint estimate

Color changes are the biggest coverage variable, so when in doubt, ask the paint desk for a primer recommendation.

Primer Considerations

Primer isn’t always required, but when it is, it’s non-negotiable.

When Primer Is Required

Scenario	Primer Type	Why
New drywall	PVA primer	Seals porous surface and evens absorption
Dark to light	Tinted primer	Blocks base color bleed
Stains from water or smoke	Stain-blocking primer	Prevents bleed-through
Bare wood	Oil-based primer	Blocks tannins and seals knots
Glossy walls	Bonding primer	Improves adhesion

When Primer Is Optional

• Light color to light color changes
• Same color touch-ups
• Previously primed walls in good condition
• Using paint-and-primer-in-one from quality brands only

Primer Coverage Rates

• PVA primer: 300 to 350 sq ft/gallon
• Stain-blocking primer: 250 to 300 sq ft/gallon due to thicker formula
• Bonding primer: 300 sq ft/gallon

Budget one gallon of primer for every 300 sq ft. For a standard bedroom with 350 sq ft of wall area, buy 1 gallon of primer plus 2 gallons of paint.

Cost Breakdown Example

For a 12×12 bedroom with 384 sq ft wall area and two coats of mid-tier paint:

Item	Quantity	Unit Cost	Total
Paint, 2 gallons	2	$45	$90
Primer, 1 gallon	1	$25	$25
Roller covers	2	$4	$8
2-inch angled brush	1	$12	$12
Painter’s tape	1 roll	$8	$8
Drop cloth	1	$15	$15
Paint tray with liner	1	$6	$6
Total Materials			$164

Labor, if hiring: $2 to $4 per sq ft equals $768 to $1,536 for professional painting.

DIY savings: over $1,200 for a weekend project.

Using the Paint Calculator

For complex rooms with vaulted ceilings, multiple windows, or accent walls, use our paint calculator to:

• Input exact dimensions in feet and inches
• Specify door and window counts
• Select paint finish type because it affects coverage
• Get separate estimates for walls and ceiling
• Calculate total cost with paint prices
• Export shopping list for the hardware store

The calculator automatically applies the correct coverage rate based on surface type and finish, and rounds to the nearest quart or gallon.

Final Checklist

Before you buy:

• Measured room length and width in feet
• Measured ceiling height from floor to ceiling minus trim
• Counted doors and windows
• Decided on one coat versus two coats
• Selected paint finish: flat, eggshell, satin, or semi-gloss
• Checked coverage rate on paint can, usually 350 to 400 sq ft/gallon
• Calculated primer separately if needed
• Added 10% buffer for waste and touch-ups
• Verified all paint from same batch code
• Bought rollers, brushes, tape, and drop cloths

Frequently Asked Questions

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

For a 12×12 room with 8-foot ceilings, you need approximately 1.5 to 2 gallons for two coats. The exact amount depends on the number of doors and windows. Wall area is roughly 384 square feet, which equals 48-foot perimeter times 8-foot height. Subtract 21 sq ft per door and 15 sq ft per window, then divide by 350 sq ft/gallon coverage. Always buy the full 2 gallons to account for texture, cut-ins, and future touch-ups.

Do I need one coat or two coats of paint?

Two coats are standard for any color change, new drywall, or when painting over stains. One coat works only for same-color touch-ups or when using premium paint over previously painted walls in excellent condition. Professional painters always apply two coats because the first coat seals and levels the surface, while the second coat provides uniform color and durability. Cutting corners with one coat leads to visible roller marks and uneven color.

How do I calculate paint for a room with high ceilings?

For rooms with ceilings 10 feet or higher, measure the actual wall height from floor to where the wall meets the ceiling. Multiply perimeter by height to get wall area, then subtract openings. Example: A 12×12 room with 10-foot ceilings has 480 sq ft of wall area, which equals 48-foot perimeter times 10 feet. After subtracting one door and two windows, you have roughly 420 sq ft. For two coats at 350 sq ft/gallon coverage, you need 2.5 gallons.

Should I subtract doors and windows from my calculation?

For small rooms under 150 sq ft, skip the subtraction because the paint saved is minimal and you’ll use it for cutting in around trim. For larger rooms over 300 sq ft, subtract doors at 21 sq ft each and windows at 15 sq ft each to avoid buying an unnecessary gallon. Each door saves about 0.06 gallons, and each window saves 0.04 gallons. In a room with 3 windows and 2 doors, that equals 0.3 gallons saved.

Why does paint coverage vary between brands?

Paint coverage depends on pigment concentration, binder quality, and solids content. Budget paints at $20 to $30 per gallon have less pigment and cover 250 to 300 sq ft/gallon. Premium paints at $50 to $70 per gallon have higher pigment loads and cover 375 to 400 sq ft/gallon. The coverage rate is printed on every can, so always check before calculating. Using the wrong coverage rate can lead to buying too little paint and making emergency store runs mid-project.

Use our paint calculator to double-check your math and ensure you buy exactly what you need with no shortages and no excess.