How to Estimate Paint Coverage for Any Room

Estimating paint is a straightforward area calculation, but most people over-order by forgetting to subtract windows and doors, or under-order by not accounting for multiple coats.

The Basic Formula

Paintable Area = (Wall Perimeter x Height) - (Door Area + Window Area)

Gallons Needed = (Paintable Area / Coverage per Gallon) x Number of Coats

Standard Coverage Rates

Paint Type	Coverage per Gallon
Interior flat/matte	350-400 sq ft
Interior eggshell/satin	300-350 sq ft
Interior semi-gloss	300-350 sq ft
Exterior latex	300-400 sq ft
Primer	250-300 sq ft

Standard Opening Deductions

Opening	Area
Standard door (3x7 ft)	21 sq ft
Standard window (3x4 ft)	12 sq ft
French door	42 sq ft

Example Calculation

For a 12x14 ft room with 8 ft ceilings, two doors, and two windows:

1. Wall perimeter: 2 x (12 + 14) = 52 ft
2. Wall area: 52 x 8 = 416 sq ft
3. Deduct openings: -2 doors (42 sq ft) - 2 windows (24 sq ft) = 350 sq ft
4. Two coats needed: 350 x 2 = 700 sq ft
5. Gallons needed: 700 / 350 = 2 gallons

Ceilings

Ceiling paint is calculated separately:

Ceiling area = Length x Width

For the example above: 12 x 14 = 168 sq ft. One gallon covers this easily.

Common Mistakes

1. Forgetting to Subtract Openings

A standard door takes up 21 sq ft. Two doors and two windows reduce your wall area by 66 sq feet - that’s nearly one-fifth of a gallon of wasted paint.

2. Not Accounting for Texture

Textured walls (popcorn, knockdown, orange peel) use 15-20% more paint than smooth walls.

3. Skipping Primer on Dark Colors

Painting a dark wall light requires primer first, otherwise you will need 3-4 coats instead of 2.

4. Assuming One Coat Is Enough

Most paint colors require two coats for even coverage. Dark reds and yellows may need three.

Pro Tips

• Buy all paint at once to ensure color consistency between cans
• Keep a quart for future touch-ups
• Use the calculator on this site for your specific room dimensions
• Account for 10% extra for touch-ups and future repairs