The Room Paint Calculator works out paint for a whole room with separate amounts for the three paints most rooms use: wall paint, ceiling paint and trim (baseboard) paint.
Room Paint Calculator
Paint for a whole room from its dimensions — separate amounts for walls, ceiling and trim.
Walls are calculated from the perimeter × height minus doors and windows; the ceiling from length × width; and trim from the perimeter × the baseboard face height. Wall and ceiling paint appear in gallons, trim paint in quarts.
Formula
- Wall paint: (2(L + W) × H − 21 ft² × doors − 15 ft² × windows) × coats ÷ wall coverage
- Ceiling paint: L × W × coats ÷ ceiling coverage
- Trim paint: 2(L + W) × trim height × coats ÷ wall coverage
How the Calculation Works
Step 1: Calculate the three surfaces separately.
Step 2: Multiply each by the number of coats.
Step 3: Divide by the coverage for each paint.
Example Calculation
Given: 14 × 12 ft room, 8 ft walls, 1 door, 2 windows, 2 coats, 350 ft²/gal for walls and ceiling, 4 in baseboard
- Walls = 416 − 21 − 30 = 365 ft² → 365 × 2 ÷ 350 ≈ 2.09 gal
- Ceiling = 168 ft² → 168 × 2 ÷ 350 = 0.96 gal
- Trim = 52 ft × 0.333 ft = 17.3 ft² → ≈ 0.10 gal ≈ 0.4 qt
Shopping list: 3 gallons (or 2 gallons + 1 quart) of wall paint, 1 gallon of ceiling paint, 1 quart of trim paint.
Why Separate the Paints?
- Ceilings are often painted with a flat ceiling paint.
- Trim usually gets a more durable semi-gloss or gloss.
- Walls may be a different color and sheen from both.
Material Estimation Notes
- The trim estimate covers baseboards only; door and window casings and doors are in the Trim & Door Paint Calculator.
- Buy whole cans and keep leftovers for touch-ups.
Frequently Asked Questions
How much paint do I need for a room?
Calculate walls, ceiling and trim separately; the example 14 × 12 room needs about 2.1 gallons for the walls.
How much ceiling paint do I need?
Ceiling area × coats ÷ coverage; a 14 × 12 ceiling needs about a gallon for two coats.
How much paint for baseboards?
Usually a quart is plenty for a single room.
Should the ceiling be painted first?
Many painters work top-down: ceiling, then walls, then trim.
Does this include the door?
No — the door is subtracted from the walls; paint it using the Trim & Door Paint Calculator.
