Paint Calculator
Estimate gallons or quarts for a room's walls and/or ceiling, accounting for doors, windows, and the number of coats. Coverage per gallon is editable — always confirm the actual figure against your specific product's label before buying.
Door and window area exceeds the wall area entered — check the counts and sizes above.
Formula: (net wall area + ceiling area) × coats ÷ coverage per gallon, rounded up to a purchasable can size (quarts under 1 gallon, whole gallons above it). Actual coverage varies by paint, surface texture, and application method — check the can label before you buy.
14 ft × 12 ft room, 8 ft walls, walls only, 1 door (21 ft²), 1 window (15 ft²), 2 coats, 350 ft² coverage per gallon: Perimeter: 2 × (14 + 12) = 52 ft Gross wall area: 52 × 8 = 416 ft² Openings: 21 + 15 = 36 ft² Net wall area: 416 − 36 = 380 ft² Exact gallons: (380 × 2) / 350 ≈ 2.17 gal Buy: 3 gallons (rounded up to a whole can)
How to use this calculator
- Choose whether you're painting the walls, the ceiling, or both.
- Enter the room's length, width, and (for walls) height in feet.
- Enter how many doors and windows the walls have, and adjust their size if yours differ from the defaults.
- Set the number of coats and the coverage per gallon your specific paint claims — this is the one figure most worth double-checking on the can.
- Read the gallons/quarts to buy, or add a price per gallon for an estimated cost.
How the calculation works
Wall area starts from the room's perimeter times wall height, then subtracts the combined area of doors and windows — those openings can never push the total below zero, so an unrealistic door/window count is flagged as a warning instead of producing a negative number. Ceiling area is simply length times width. The combined paintable area is multiplied by the number of coats and divided by the coverage figure to get an exact gallon count, which is then rounded up to a size you can actually buy: quarts in 0.25-gallon steps below one gallon, whole gallons above it.
FAQ
Why does the can say a different coverage than the 350 ft² default?
Coverage depends on the paint formula, sheen, and the surface being painted — a textured or unprimed wall can absorb noticeably more. Always use the figure printed on your specific can, not a generic default.
Why does it round up instead of showing the exact decimal?
Paint is sold in fixed can sizes, so the exact decimal amount isn't purchasable — the tool shows both the exact figure and the realistic amount to buy.
Does the ceiling calculation subtract anything?
No — door and window subtraction only applies to walls. Ceiling area is the full length times width.