Measure visible painted faces. Door and window counts use editable linear-foot allowances so unusual casing sizes remain explicit.
01 / Formula
How this is calculated
Gallons = total trim length × trim width ÷ 12 × coats ÷ coverage02 / Assumptions
What the estimate assumes
- ✓Trim width represents the painted face.
- ✓Door and window trim lengths are editable averages.
- ✓Returns, edges, detailed profiles and application loss may increase usage.
03 / Worked example
See the math in context
Three hundred linear feet of 3.5-inch trim has 87.5 sq ft of face area, or 175 coated sq ft for two coats.
04 / Guidance
Measure profiles deliberately
Deep or ornate profiles have more surface than face width alone suggests. Increase the entered width or use a measured coverage rate when detail is substantial.
Questions
Frequently asked
Should I round up when buying paint?+
Yes. Paint is sold in fixed container sizes, and a small reserve helps with touch-ups, porous surfaces, and application loss. The calculator shows both the theoretical quantity and a practical purchase amount.
Does paint coverage include two coats?+
Coverage printed on a can is normally stated per coat. Two coats cover the same surface twice, so the calculator multiplies net area by the number of coats before dividing by the selected coverage rate.