# Paint Trim Calculator

Paint trim calculator for baseboards, crown molding, and door and window casings. Includes exterior paint trim calculator option for fascia and soffits. Gallons, cost, and coats.

## What this calculates

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.

## Inputs

- **Baseboard** (linear ft) — min 0 — Total baseboard length (room perimeters)
- **Baseboard Height** (in) — min 0 — Standard baseboard is 3-5 inches; modern homes often 5-7 inches
- **Crown Molding** (linear ft) — min 0 — Set to 0 if no crown. Usually equals baseboard length.
- **Door Openings (casing and doors)** — min 0, max 50 — Counts both sides of the jamb + head casing per door
- **Window Openings (casing)** — min 0, max 50
- **Trim Scope** — options: Interior trim (baseboard, casing, crown), Exterior paint trim calculator (fascia, soffit, casing) — Exterior trim uses lower coverage rate for rough surfaces
- **Coverage Rate** (sq ft/gal) — min 150, max 500 — Trim enamel covers 400 sq ft/gal (interior), 300 sq ft/gal (exterior)
- **Number of Coats** — min 1, max 4 — 2 coats standard for glossy trim; 3 for very dark-to-light changes
- **Trim Paint Price per Gallon** ($) — min 0 — Interior trim enamel $50-80/gal; exterior trim $55-90/gal

## Outputs

- **Baseboard Area** (sq ft)
- **Crown Molding Area** (sq ft)
- **Door Trim Area** (sq ft)
- **Window Trim Area** (sq ft)
- **Total Trim Area** (sq ft)
- **Gallons Needed (exact)** (gal)
- **Gallons to Order** (gal)
- **Estimated Cost** — formatted as currency

## Details

## 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:

1. **Lower coverage rate** (around 300 sq ft/gal instead of 400) because exterior paint is thicker-bodied for UV and weather resistance.
2. **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

1. **Measure baseboard height.** A 3-inch baseboard uses less paint than a 7-inch craftsman baseboard. The calculator scales baseboard area by height.
2. **Count every door opening.** Even closet doors have casing on both sides of the jamb.
3. **Add crown only where it exists.** Crown is often skipped in bedrooms and bathrooms; do not auto-include it.
4. **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.
5. **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.

## Frequently Asked Questions

**Q: How much paint do I need for interior trim?**

A: For a 2,000 sq ft home with 400 linear ft of baseboard, 12 doors, and 16 windows, expect 400-500 sq ft of trim surface area. At 400 sq ft per gallon trim enamel coverage and 2 coats, that is 2-2.5 gallons. Buy 3 gallons for a full interior trim repaint, which leaves half a gallon for touch-ups over the life of the paint job.

**Q: How does the exterior paint trim calculator differ?**

A: Exterior paint trim calculator mode drops coverage to 300 sq ft/gal (from 400 interior) and adds 20% to the trim area for rougher fascia, soffit, and casing surfaces. Exterior trim paint is thicker and more UV-resistant, and the rougher lumber profile absorbs more. Switch the scope selector to 'Exterior' to apply both adjustments automatically.

**Q: How do I calculate the area of baseboard?**

A: Multiply baseboard linear feet by the baseboard height (in feet) to get the face area, then add 25% for the top bevel and rounded bottom. For 300 linear ft of 4-inch baseboard: 300 x (4 / 12) x 1.25 = 125 sq ft. That is the area of paint needed per coat. Multiply by coats and divide by coverage rate to get gallons.

**Q: How much does door trim paint cover?**

A: A standard door opening (6'8" x 3') with 3.5" wide casing on both sides of the jamb and across the head equals about 6 sq ft of trim area. French doors and wide entry doors can be 10-12 sq ft. Sliding glass doors typically have minimal trim (most is covered by the door itself). The calculator uses 6 sq ft per standard door opening.

**Q: Is trim paint different from wall paint?**

A: Yes. Trim enamel (interior) is typically water-based alkyd or 100% acrylic with high solids, leveling additives for a smooth finish, and a semi-gloss or satin sheen. It costs $55-85/gal versus $45-70/gal for wall paint. Trim paint is designed to show fewer brush marks and stand up to scuffing. Never substitute wall paint for trim or vice versa; you will get obvious finish differences at inside corners.

**Q: Should I caulk before painting trim?**

A: Yes, every inside corner and gap between trim and wall needs a bead of paintable caulk (acrylic latex, not silicone). Caulk after primer, before topcoat. A tube of good painter's caulk runs $4-6 and covers about 40-60 linear feet. A whole-house trim repaint uses 6-10 tubes of caulk ($30-60). The calculator does not factor this, but always budget for it.

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Source: https://vastcalc.com/calculators/construction/paint-trim
Category: Construction
Last updated: 2026-04-08