Understanding your result
The headline is the trim paint for the coats you chose, with the allowance, and the sub-line is the can list. The three figures show the trim area, the paint per coat and the cans.
The breakdown lists each kind of trim with its area: fascia, soffit, rake boards, corner boards on both faces, and the casings with the door and window counts. Those lines tell you where the paint is going, and the soffit is normally the largest. Then come the coverage, coats, allowance, total and can lines in the usual form.
Trim is painted after the siding and in a contrasting colour, so it is a separate purchase from the exterior house paint calculator’s figure. The garage door calculator includes its own frame trim, so do not count that doorway here. The interior face of the window frames is in the window frame calculator, with interior enamel, and a shed’s trim is inside the shed paint calculator.
How we calculate this
Each run of trim is a strip: its length in feet times its width in inches, divided by 12 for square feet (metres and centimetres in metric mode). Corner boards show two faces, one on each wall, of 5.5 in nominal stock. The casing figures are derived from a 36 × 80 in door with 2 in brickmould and a 4.5 in jamb (about 8 sq ft on the outside) and a 3 × 5 ft window with 3.5 in casing and a sill (about 6 sq ft); the trim and doors guide shows how to measure your own and the standard sizes page lists the openings they are based on.
Coverage is the trim paint’s figure from the can, 350 to 400 sq ft per gallon for exterior acrylics; the coverage rates table has the published figures. The allowance is 10% for brush and roller work from a ladder, where paint dries in the cup and on the brush between moves; the exterior measuring guide explains how to measure the eaves without climbing.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Coverage | 350 sq ft per gallon | Exterior acrylic and trim paint data sheets (Sherwin-Williams, Benjamin Moore, Behr): 350–400 on smooth, primed trim |
| Fascia width | 8 in | Common 1 × 8 fascia; 6 and 10 in are also common |
| Soffit depth | 16 in | A typical eave overhang; 12 to 24 in in practice |
| Corner board | 5.5 in, two faces | 1 × 6 nominal stock |
| Door casing, outside | 8 sq ft | Derived: 2 in brickmould and 4.5 in jamb on a 36 × 80 in door |
| Window casing, outside | 6 sq ft | Derived: 3.5 in casing and sill on a 3 × 5 ft window |
| Coats | 2 | Manufacturers’ recommendation for a full repaint |
| Allowance | 10% | Brush loss working from a ladder; 25–35% if spraying |
Assumptions last reviewed October 7, 2026.
The calculator does not model primer, which bare, weathered or filled trim needs (the primer calculator in its area mode gives the quantity), gutters, which are usually not painted, or shutters, which are a door-sized quantity each side and can be entered as extra doors. It does not count porch columns or railings.
Two worked examples
A typical single-storey house
160 ft of 8 in fascia and 16 in soffit, 60 ft of 8 in rake boards, four 18 ft corner boards, two doors and ten windows, two coats at 350 sq ft per gallon.
- Fascia: 160 × 8 ÷ 12 = 107 sq ft; soffit: 160 × 16 ÷ 12 = 213 sq ft
- Rakes: 60 × 8 ÷ 12 = 40 sq ft; corners: 4 × 18 × 5.5 ÷ 12 × 2 = 66 sq ft
- Casings: 2 × 8 + 10 × 6 = 76 sq ft
- Trim area: 502 sq ft
- Per coat: 502 ÷ 350 = 1.434 gallons
- Needed: 1.434 × 2 × 1.10 = 3.16 gallons, buy 3 gallons + 1 quart
Three gallons and a quart, or four gallons with touch-up to spare. The soffit alone is more than two-fifths of the job, and the result’s note suggests spraying it.
A large two-storey house with deep eaves
200 ft of 10 in fascia and 24 in soffit, 80 ft of rakes, six 20 ft corner boards, three doors and eighteen windows, two coats.
- Fascia: 167 sq ft; soffit: 400 sq ft; rakes: 53 sq ft
- Corners: 110 sq ft; casings: 132 sq ft
- Trim area: 862 sq ft
- Per coat: 862 ÷ 350 = 2.463 gallons
- Needed: 2.463 × 2 × 1.10 = 5.42 gallons, buy a 5-gallon pail + 2 quarts
The casings alone, three doors and twelve windows given one coat as a refresh, would be 96 sq ft and 1.1 quarts: two quarts to buy, which is why a touch-up of the casings is a quart job and a full trim repaint is a pail.
Where to find your inputs
Fascia and soffit length. The eaves: the perimeter for a hipped roof, the two long sides for a gable roof. Measure along the ground under the eave.
Widths and depths. Measure one fascia board and one soffit with a tape from a ladder, or read them from the plans. Fascia is the face board; soffit is the underside from the wall to the fascia.
Rakes. The sloping boards along the gable ends. Length is the slope: for a 30 ft gable with a 6-in-12 pitch each rake is about 16.8 ft, so 33.5 ft per gable end.
Corner boards. Count outside corners (and inside ones if they are trimmed) and measure their height from the foundation to the eave.
Doors and windows. Count openings with exterior trim; garage doors are in their own calculator.
Common mistakes
- Forgetting the soffit. It is the biggest line and the one you cannot see from the street.
- Counting corner boards once. Each one has two faces.
- Using interior enamel outside. It chalks and cracks within a year. Exterior acrylic only.
- Painting over bare or weathered wood without primer. The topcoat peels there first.
- Spraying with a brushing allowance. Overspray on narrow trim is a third of the paint.
- Painting aluminium fascia without a bonding primer. Ordinary paint flakes off the factory finish.
Questions people ask
- How much paint does exterior trim take?
- A house with 160 ft of 8 in fascia and 16 in soffit, 60 ft of rake boards, four 18 ft corner boards, two doors and ten windows has about 500 sq ft of trim. Two coats at 350 sq ft per gallon with a 10% allowance come to 3.16 gallons, so three gallons and a quart.
- How do I measure fascia and soffit?
- Both run along the eaves, so their length is the house perimeter for a hipped roof, or the two long sides for a gable roof (the gable ends have rake boards instead). The fascia width is the board's face, typically 6 to 10 in; the soffit depth is the overhang, typically 12 to 24 in. Measure one spot of each and apply it to the length.
- Why is the soffit the biggest line?
- Because it is wide. A 16 in soffit is twice the area of an 8 in fascia on the same length, and it is painted overhead. Vented soffit panels take about the same paint as solid ones and twice the time, and are the strongest case for a sprayer on trim.
- What are the casing figures?
- The outside face of the trim around an opening. A door's brickmould and jamb is about 8 sq ft; a window's casing and sill about 6 sq ft. Wide colonial casings or deep jambs are more; the trim and doors guide shows how to measure one and scale the rest.
- Which paint for exterior trim?
- An exterior acrylic trim paint or a 100% acrylic exterior paint in satin or semi-gloss, which sheds water and cleans. Bare wood needs an exterior primer first; aluminium fascia needs a bonding primer; vinyl trim needs a paint rated for vinyl in a light colour.
- Should I spray or brush the trim?
- Brush and a small roller for fascia and corners, where masking the siding would take longer than brushing; a sprayer for soffits, especially vented ones. Spraying adds 25 to 35% to the paint; set the allowance accordingly.