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Paint Calculator

Estimate exactly how many gallons of paint you need for any room. Account for doors, windows, multiple coats, and ceiling paint. No more guessing at the hardware store.

Room Dimensions

Save Room

Paint Estimate

Paintable Wall Area
368sq ft
Gallons Needed (2 coats)
3gallons
Gross wall area416 sq ft
Less doors (2)-42 sq ft
Less windows (2)-24 sq ft
Total with waste368 sq ft

Shopping List

Paint (2 coats)3 gallons
Primer (recommended)2 gallons
Painter's tape (rolls)1 roll

How to Calculate Paint Coverage

Calculating paint is a straightforward area subtraction problem:

  1. Find your wall area: Multiply the room perimeter (2 x (length + width)) by the wall height.
    Wall Area = 2 x (Length + Width) x Height
  2. Subtract openings: Deduct the area of doors (21 sq ft each) and windows (12 sq ft each).
  3. Add ceiling if needed: Length x Width for the ceiling area.
  4. Multiply by coats: Multiply by the number of coats. Most jobs need 2 coats.
    Gallons = (Net Area x Coats) / 350

Example Calculation

Let's calculate paint for a 12x14 ft bedroom with 8-ft ceilings, 2 doors, and 2 windows, with 2 coats:

  • Perimeter: 2 x (12 + 14) = 52 ft
  • Gross wall area: 52 ft x 8 ft = 416 sq ft
  • Less doors: 2 x 21 = 42 sq ft
  • Less windows: 2 x 12 = 24 sq ft
  • Net wall area: 416 - 66 = 350 sq ft
  • Two coats: 350 x 2 = 700 sq ft
  • Gallons needed: 700 / 350 = 2 gallons

Common Mistakes in Paint Estimation

  • Forgetting to subtract doors and windows: Two doors and two windows reduce your wall area by 66 sq ft — nearly a fifth of a gallon of wasted paint.
  • Not accounting for textured walls: Popcorn, knockdown, and orange-peel textures consume 15-20% more paint than smooth walls.
  • Assuming one coat is enough: Most colors require two coats. Dark reds and yellows may need three. Always buy enough for two coats.

Frequently Asked Questions

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

A 12x12 room with 8-ft ceilings, one door, and one window needs about 1.5 gallons for one coat or 3 gallons for two coats, including ceiling paint if desired.

How many square feet does a gallon of paint cover?

One gallon of interior paint typically covers 350-400 square feet. Higher quality paints often have better coverage. Dark colors and textured surfaces may need more paint.

Do I need primer before painting?

Primer is recommended when painting over dark colors, new drywall, or stained surfaces. For most repaints of similar colors, two coats of paint without primer is sufficient.