Paint Trim Calculator
Trim paint is expensive ($60-90/gal for quality enamel) and trim surfaces are the most visible finish in a room, so buying too little or too much hurts. This paint trim calculator adds up baseboards, crown molding, and door plus window casings, applies the right coverage rate, and tells you how many gallons to order. Use the exterior paint trim calculator mode for fascia, soffits, and exterior window casings.
How to Calculate Trim Paint
Trim paint area is not trim linear feet. You need the painted surface area, which depends on the face width and the number of surfaces (top, face, bottom). The calculator converts your trim linear feet to surface area using these conventions:
- Baseboard: linear feet x height (inches to feet) x 1.25 (face plus top bevel)
- Crown molding: linear feet x 4 inches x 1.5 (angled face, top and bottom edges)
- Door casing: 6 sq ft per opening (both jamb sides + head, 3.5" wide casing, 7 ft tall)
- Window casing: 4 sq ft per window (all 4 sides, 3.5" wide)
Add those areas, multiply by coats, divide by coverage rate (400 sq ft/gal for interior trim enamel, 300 sq ft/gal for exterior paint).
Interior vs Exterior Paint Trim Calculator
An exterior paint trim calculator needs two adjustments beyond the interior version:
- Lower coverage rate (around 300 sq ft/gal instead of 400) because exterior paint is thicker-bodied for UV and weather resistance.
- Rougher surfaces (fascia, soffit, rafter tails) need about 20% more paint than smooth interior casing.
Switch the scope selector to Exterior to apply both adjustments. Typical exterior trim paint covers 250-350 sq ft/gal depending on the profile and weathering.
Example: Whole-House Interior Trim Repaint
A 2,000 sq ft home typically has:
- Baseboard: 300-400 linear feet at 4" tall = 125-170 sq ft
- Crown molding (if installed): 200-300 linear feet = 100-150 sq ft
- Doors: 10-15 openings at 6 sq ft each = 60-90 sq ft
- Windows: 15-20 at 4 sq ft each = 60-80 sq ft
- Total: 345-490 sq ft of trim area
At 2 coats and 400 sq ft/gal, that is 1.7-2.5 gallons of trim paint. Buy 3 gallons to cover touch-ups and a future room.
Cost to Paint Interior Trim
| Home Size | Trim Area | DIY Cost | Pro Cost |
|---|---|---|---|
| 1,200 sq ft | 250-350 sq ft | $130-200 | $800-1,500 |
| 2,000 sq ft | 400-500 sq ft | $200-300 | $1,400-2,500 |
| 3,500 sq ft | 700-900 sq ft | $350-450 | $2,500-4,500 |
DIY cost is paint plus brushes and sandpaper (~$40). Pro cost includes caulking, minor wood repair, and two coats of premium enamel.
Tips for Calculating Trim Paint
- Measure baseboard height. A 3-inch baseboard uses less paint than a 7-inch craftsman baseboard. The calculator scales baseboard area by height.
- Count every door opening. Even closet doors have casing on both sides of the jamb.
- Add crown only where it exists. Crown is often skipped in bedrooms and bathrooms; do not auto-include it.
- Trim enamel is not wall paint. It has higher solids, a slower cure, and leveling additives for a smooth finish. Do not use wall paint for trim, and do not use trim paint for walls.
- Primer on new trim. New MDF or pine trim needs a dedicated primer (often oil-based) before topcoat. Add 1 extra gallon of primer for the same area calculation.