How Much Paint Do I Need for a 12x12 Room? (Gallon Calculations)

A standard $12 \times 12\text{ foot}$ bedroom or office is one of the most common residential spaces homeowners choose to repaint.

The short answer is: you will need 2 gallons of paint for two coats on the walls of a standard $12 \times 12\text{ room}$ with $8\text{-foot}$ ceilings. If you are also painting the ceiling, purchase an additional 1 gallon of specialized ceiling paint.

This guide explains how to calculate the paintable square footage of your walls and ceiling so you can get the perfect amount of paint.

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The Gallons-to-Square-Foot Coverage Rule

Before running calculations, know that a standard gallon of paint covers between 350 and 400 square feet of smooth wall surface.

• 1 Gallon = 350 sq ft (used as a safe, practical estimate)
• 2 Coats = Doubling your square footage calculation

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Step-by-Step Wall Estimation for a 12x12 Room

Let’s walk through the math for a room that is $12\text{ ft}$ long, $12\text{ ft}$ wide, and has $8\text{-foot}$ ceilings.

Step 1: Calculate the Perimeter of the Room

Add all four wall lengths together: $$\text{Perimeter} = 12\text{ ft} + 12\text{ ft} + 12\text{ ft} + 12\text{ ft} = 48\text{ ft}$$

Step 2: Calculate Gross Wall Area

Multiply the perimeter by the wall height: $$\text{Gross Area} = 48\text{ ft} \times 8\text{ ft} = 384\text{ sq ft}$$

Step 3: Subtract Doors and Windows

You don’t paint window panes or doors, so subtract them from the gross area.

• Standard Entry Door: Subtract $21\text{ sq ft}$
• Standard Window: Subtract $15\text{ sq ft}$ (typically 3x5 ft)

Let’s assume the room has 1 door and 1 window: $$\text{Net Paintable Area} = 384\text{ sq ft} - 21\text{ sq ft} - 15\text{ sq ft} = 348\text{ sq ft}$$

Step 4: Account for Multiple Coats

Most professional results require 2 coats of paint. $$\text{Total Coverage Needed} = 348\text{ sq ft} \times 2 = 696\text{ sq ft}$$

Step 5: Convert to Gallons

Divide the total coverage needed by 350 (average coverage per gallon): $$\text{Gallons Required} = 696 \div 350 = 1.99\text{ gallons}$$ Round up to the nearest whole gallon: 2 gallons.

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12x12 Room Paint Coverage Lookup Table

Wall heights differ by building construction. Here is how many gallons of paint you need for a 12x12 room under varying wall heights (assuming 1 door, 1 window, and 2 coats of paint):

Ceiling Height	Gross Wall Area	Net Area (After Deductions)	Total Area (2 Coats)	Gallons Required
8 Feet	$384\text{ sq ft}$	$348\text{ sq ft}$	$696\text{ sq ft}$	2 Gallons
9 Feet	$432\text{ sq ft}$	$396\text{ sq ft}$	$792\text{ sq ft}$	2.5 Gallons (Order 3)
10 Feet	$480\text{ sq ft}$	$444\text{ sq ft}$	$888\text{ sq ft}$	3 Gallons

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Ceiling Calculations

If you plan to paint the ceiling as well, calculate its square footage separately: $$\text{Ceiling Area} = \text{Length} \times \text{Width}$$ $$\text{Ceiling Area} = 12\text{ ft} \times 12\text{ ft} = 144\text{ sq ft}$$

Since one gallon covers 350 sq ft, 1 gallon of ceiling paint will easily cover the ceiling with two coats.

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Material Purchase List for a 12x12 Room

If you are painting walls, ceiling, and trim, here is a standard shopping list:

1. Wall Paint: 2 Gallons
2. Ceiling Paint: 1 Gallon
3. Trim & Baseboard Paint: 1 Quart (standard semi-gloss/gloss)
4. Primer: 1 Gallon (only needed if changing colors drastically or painting raw drywall)

For a customized estimate that subtracts custom window sizes and calculates trim or baseboards, use our Interior Paint Calculator.