Paint Calculator – How Much Paint Do I Need? | CalcLoft
Find out exactly how many gallons of paint you need for any room — including doors, windows and number of coats.
How to measure a room for painting
To find the wall area of a rectangular room, add the length of all four walls and multiply by the wall height:
Wall area = (length + width) × 2 × wall height
For example, a 12 × 12 ft room with 8 ft walls has (12 + 12) × 2 × 8 = 384 sq ft of wall surface. Subtract roughly 21 sq ft per standard door and 12 sq ft per standard window.
How much paint covers one gallon?
| Surface | Coverage per gallon |
|---|---|
| Smooth, primed drywall | 350–400 sq ft |
| Textured or unprimed drywall | 250–300 sq ft |
| Wood or previously painted surfaces | 300–350 sq ft |
| Masonry / rough surfaces | 200–250 sq ft |
How much paint for a 12x12 room?
For a 12 × 12 ft bedroom with 8 ft walls, one door, one window and two coats, you need about 2 gallons of paint. A quart will usually cover touch-ups. Use the calculator above to check your exact room.
Paint calculator FAQ
Should I buy extra paint?
Yes — buy about 10% extra. It covers mistakes, touch-ups later, and matching issues if the store discontinues the color.
Does ceiling paint count?
No. The calculator estimates walls only. Ceilings usually need one coat of ceiling paint — roughly one gallon per 300–400 sq ft.
Why do I need two coats?
Two coats give even color, better durability and hide the old color. Darker or saturated colors may even need three coats.
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