Trim and Door Paint Calculator

How it works

Trim is bought by the linear foot but painted by the square foot. The painted area of baseboard or casing is its length times its face width; with the width in inches that is linear feet × width ÷ 12. Window trim is added as linear feet per window at the same face width.

Each door slab adds its width times its height for every side painted. A standard 36 × 80 in door is 2,880 sq in, or 20 sq ft per side, so a door painted on both sides is 40 sq ft.

The total is multiplied by the number of coats and divided by the coverage of the enamel. Trim jobs are often small, so the result is shown in quarts (a quarter gallon) as well as whole gallons.

Formula

linear feet   = baseboard and casing + windows × trim per window
trim area     = linear feet × face width (in) ÷ 12
door area     = doors × sides × width (in) × height (in) ÷ 144
total area    = (trim area + door area) × coats
enamel (gal)  = total area ÷ coverage per gallon
quarts to buy = enamel × 4, rounded up; gallons to buy = enamel, rounded up

Example

120 ft of 3.5 in baseboard and casing plus four windows with 16 ft of trim each is 184 linear feet, or 184 × 3.5 ÷ 12 = 53.67 sq ft. Three 36 × 80 in doors painted on both sides add 3 × 2 × 20 = 120 sq ft.

Two coats on 173.67 sq ft is 347.33 sq ft. At 400 sq ft per gallon that is 0.87 gallon: 4 quarts, or 1 gallon.

Assumptions and limitations

• Trim is treated as a flat face of the width entered. Profiled molding has more surface than its flat width, so the result is low for heavily profiled trim unless a wider face is entered.
• Door slabs are flat rectangles. Panel doors have more surface, and edges are not counted. Door frames (jambs and stops) are not included unless their length is added to the trim length.
• Coverage is a typical value and editable. Enamel data sheets give a range, and the manufacturer states the actual spread rate depends on surface texture and porosity.
• Primer for bare wood or a change of sheen is not included.
• The result is an estimate and not a substitute for the paint manufacturer's instructions.

Frequently asked questions