Interior paint calculator
Estimate how many gallons of interior paint you need for walls, ceiling, trim, and doors. Enter the room's dimensions and openings; the calculator returns the exact paint plan with Kompozit pricing.
Estimates round up to the nearest quart and are based on Kompozit's published coverage. Buy slightly more for touch-ups and color changes.
The math behind the estimate
Wall area = perimeter (2 × length + 2 × width) × ceiling height. We subtract 21 sq ft per door and 15 sq ft per window. The result is multiplied by the number of coats and divided by the paint's coverage rate (Kompozit ONE covers ~388 sq ft per gallon). The final number is rounded up to the nearest quart, since paint sells in 1-qt increments.
When to use 1 vs. 2 vs. 3 coats
- 1 coat: repaint in the exact same color, freshening up rather than changing.
- 2 coats: default for most jobs, including same-family color changes (beige to tan).
- 3 coats: dark over light, vivid reds and yellows that always need extra hide, or any color shift over an unprimed surface.
Why we recommend Kompozit ONE for interior
ONE is a 2-in-1 paint and primer rated for one-coat coverage on most repaints. The ~388 sq ft/gal coverage is on the high end for residential interior — meaning you buy slightly less paint than you would with a thinner big-box premium. For deeper hue changes, plan for two coats.
FAQ
Always. Running short mid-job is far worse than having a half-gallon left over for touch-ups. The calculator already rounds up to the nearest quart.
Trim is a separate calculation — most homeowners use a quart of semi-gloss or satin to do all the trim in a typical room. The wall calculator subtracts door and window area; we don't add trim paint into the wall total because the finish is usually different.
Tick the "paint ceiling" checkbox and the calculator adds the ceiling area to the total. Ceilings are typically painted in flat to hide imperfections.
For a 12×14 room, two extra doors or windows changes the gallons needed by less than 0.1 — well within rounding. If you have a wall that's mostly glass, model it as a smaller room.