Paint Calculator
How much paint do I need? Enter room length, width, and wall height to get paintable area, gallons after coats and waste, and a recommended purchase quantity.
Calculator
How it works
We convert room dimensions to feet and multiply the perimeter by wall height for gross wall area. Standard interior doors (21 sq ft) and windows (15 sq ft) are subtracted. That paintable area is multiplied by coats, divided by the coverage you enter, then increased by your waste factor. Recommended purchase rounds up to the next whole gallon.
Formula
Wall area = 2 x (length + width) x height. Paintable area = wall area − (doors x 21) − (windows x 15). Exact gallons = paintable area x coats / coverage. With waste = exact gallons x (1 + waste%). Recommended purchase = ceil(with waste).
Example
A 12 ft x 10 ft room, 8 ft walls, 2 doors, 2 windows, 2 coats, 350 sq ft per gallon, 10% waste: walls 352 sq ft − 72 sq ft openings = 280 sq ft; after coats 560 sq ft; exact 1.60 gallons; with waste 1.76; recommended purchase 2 gallons.
How to measure
Measure the room length and width, then wall height from floor to ceiling. Count interior doors and typical windows. Do not include the ceiling unless you will paint it separately. Read coverage from the paint can rather than assuming a number.
FAQ
How much paint do I need for a 12x10 room?
For 8 ft walls, two standard doors, two windows, two coats, and 350 sq ft per gallon with 10% waste, this calculator recommends 2 gallons. Change coats or coverage to match your product.
What coverage should I enter?
Use the square feet per gallon printed on the can. 350 is a common interior default; primers and rough walls often cover less.
Does this include the ceiling?
No. This version estimates wall paint only. Add ceiling area separately if you will paint it with the same product.