Trim Paint Calculator
Calculate how much paint you need for baseboards, crown molding, door frames, and other trim.
Enter linear feet and trim width.
Painting trim and molding requires separate calculation from wall painting because coverage rates, paint types, and surface areas differ significantly. Trim paint (typically semi-gloss or gloss) covers 350–400 sq ft per gallon, while flat wall paint covers 400–450 sq ft.
Total trim length formula: Total Linear Feet = Baseboard + Door Casing + Window Casing + Crown Molding
Baseboard (all perimeter walls minus doorways): Baseboard Length = Room Perimeter − (Number of Doorways × 36")
Door casing (both sides per door): Door Casing = Number of Doors × 2 sides × (2 × Door Height + Door Width) Standard interior door: 6'8" height, 32"–36" width. Per door (one side): 2 × 80" + 32" = 192" = 16 linear feet Both sides: 32 linear feet per door.
Window casing: Window Casing = Number of Windows × (2 × Window Height + Window Width)
Surface area conversion: Most trim is 2.5"–5.5" wide. For paint calculation: Trim Area (sq ft) = Total Linear Feet × (Average Trim Width in inches / 12)
Paint needed: Gallons = Trim Area / Coverage Rate (sq ft/gallon) Coverage rate: 350–400 sq ft per gallon for trim paint (semi-gloss).
Worked example: Living room: 15 ft × 18 ft, 9 ft ceilings. 2 doors, 3 windows. 3.5" baseboard, 2.5" crown molding.
Room perimeter = 2 × (15 + 18) = 66 ft Baseboard = 66 − (2 × 3) = 60 linear ft Crown molding (full perimeter) = 66 linear ft Door casing (2 doors, both sides) = 2 × 32 = 64 linear ft Window casing (3 windows, ~28 wide × 48 tall) = 3 × (2×4 + 2.33) = 31 linear ft Total linear feet = 60 + 66 + 64 + 31 = 221 linear ft Average trim width = 3.5": Area = 221 × (3.5/12) = 64.4 sq ft Paint needed = 64.4 / 375 = 0.17 gallons → buy 1 quart (32 oz) with enough for a second coat.