Paint Calculator
Enter your room's dimensions. We'll tell you the paintable area and the exact amount of paint to buy.
Advanced options
- Wall area
- 0 sq ft
- Ceiling area
- 0 sq ft
- Total paintable
- 0 sq ft
- With waste factor
- 0 sq ft
- One-coat amount
- 0
- Estimated cost
- —
How the paint calculator works
For a rectangular room, the paintable wall area is 2 × (length + width) × height. We subtract a standard area per door and per window. If you include the ceiling, we add length × width.
That gives you the one-coat paintable area. Multiply by the number of coats, divide by coverage per container, and add a 10% waste factor for spills, roller loading, and touch-ups. We round up to whole containers because paint stores don't sell fractions.
When to bump the waste factor
Bump to 15% if the surface is textured (stucco, popcorn ceiling) or porous (new drywall, unprimed wood). Bump to 20% if you're spraying instead of rolling. Keep 10% for previously painted interior walls.
Coverage numbers to know
- Imperial: 350 sq ft / gallon · Metric: 9 m² / liter — typical for latex on a primed smooth surface.
- 250–300 sq ft / gallon · 6.5–7.5 m² / liter — textured walls or flat-to-matte finishes.
- 200 sq ft / gallon · 5 m² / liter — exterior stucco, brick, or heavily porous surfaces.
- 400+ sq ft / gallon · 10+ m² / liter — premium paints on smooth previously-painted surfaces.
Common questions
Do I need primer?
If you're going lighter over darker, painting new drywall, or covering stains — yes. Primer is roughly the same coverage as paint. Add one extra container per room for primer, or bump the "coats" field from 2 to 3.
Why round up to whole containers?
Paint stores sell by the gallon (or quart for trim, by the liter in metric). Running out mid-project means a second trip, and the tint on a freshly-mixed container can shift slightly — which matters on a wall. Buying one extra is the cheap safety margin.
What about trim?
This calculator focuses on wall/ceiling coverage. For baseboards, door casings, window casings, and door faces, use the trim paint calculator — trim paint is a different product (usually semi-gloss) and is sized in quarts (or 1 L cans) rather than gallons.