Calculate walls for a rectangular room, then adjust coats and coverage for your chosen paint.
01 / Formula
How this is calculated
Paint = (((2 × length + 2 × width) × height − openings) × coats) ÷ coverage02 / Assumptions
What the estimate assumes
- ✓The room is rectangular.
- ✓Ceilings and trim are not included.
- ✓Doors and windows use editable counts with standard area allowances.
03 / Worked example
See the math in context
A 12 × 14 ft room with 8 ft ceilings has 416 sq ft of wall area before openings. With one door, two windows, and two coats, it needs about 1.95 gallons at 350 sq ft/gal.
04 / Guidance
Calculate rooms separately
Separate estimates are easier to match to different colors and finishes. Add the final purchase quantities only when rooms use the exact same paint.
Questions
Frequently asked
Should I round up when buying paint?+
Yes. Paint is sold in fixed container sizes, and a small reserve helps with touch-ups, porous surfaces, and application loss. The calculator shows both the theoretical quantity and a practical purchase amount.
Does paint coverage include two coats?+
Coverage printed on a can is normally stated per coat. Two coats cover the same surface twice, so the calculator multiplies net area by the number of coats before dividing by the selected coverage rate.