Trim and Door Paint Example: Two Doors and Baseboard Worked to One Gallon

Two new flat interior doors, their jambs and casings, and 60 ft of new baseboard need 127.57 ft2 of paint surface. At two coats of Benjamin Moore Advance Semi-Gloss, that is 255.15 ft2 of coated surface, 0.64 gallon exact at the low-end rate, so the enamel order is 1 gallon. One coat of primer covers the same 127.57 ft2, ordered as its own line at the primer label rate. Every number below is shown, so the same steps work for a different room. The figures here are worked fixtures, not project quantities.

What is being painted?

The job is a hallway with two identical flat interior doors and one run of baseboard. Both doors are new bare wood, so the primer line is a full coat. The enamel is Benjamin Moore Advance Semi-Gloss, planned as two coats at its low-end rate of 400 ft2 per gallon.

The trim and door measuring guide shows how each of these lines is taken. The partition rule matters on the casing line: the side pieces run to the underside of the head piece, and the head piece spans the full outer width, so no corner is counted twice.

How does the area add up?

Convert inches to feet first: 30 in is 2.5 ft, 80 in is 6.6667 ft, 1.375 in is 0.1146 ft, 4.5 in is 0.375 ft, 3.5 in is 0.2917 ft, and 5.25 in is 0.4375 ft.

1. One door slab: 2.5 × 6.6667 = 16.67 ft2 per side, × 2 sides = 33.33 ft2.
2. One door edges: (13.3333 + 2.5) × 0.1146 = 1.81 ft2, top and sides only.
3. One jamb: 15.8333 × 0.375 = 5.94 ft2.
4. One casing: 16.4167 × 0.2917 = 4.79 ft2 per side, × 2 sides = 9.58 ft2.
5. One door total: 33.33 + 1.81 + 5.94 + 9.58 = 50.66 ft2.
6. Two doors: 50.66 × 2 = 101.32 ft2. Baseboard: 60 × 0.4375 = 26.25 ft2.
7. Total: 101.32 + 26.25 = 127.57 ft2. Metric check: 127.57 × 0.09290304 = 11.85 m2.

The slab lines alone give 66.66 ft2. A plan built on the slab figure alone would miss 60.91 ft2 of edges, jambs, casings, and baseboard.

How much enamel do two coats need?

Multiply the total by the coat count, then divide by the product rate. Use the low end of the range for the order, because it buys the most paint the label allows for.

Enamel area = 127.57 × 2 = 255.15 ft2

Exact volume, low end = 255.15 ÷ 400 = 0.6379 gallon

In quarts: 0.6379 × 4 = 2.55 quarts, so buy 3 quarts, or 1 gallon. At the high end of 500 ft2 per gallon, the same two coats need 255.15 ÷ 500 = 0.5103 gallon, still under 1 gallon.

Result: 1 gallon of Benjamin Moore Advance Semi-Gloss enamel. The gallon is the order because the exact volume sits between 0.51 and 0.64 gallon across the label range, and paint is bought in whole containers.

What about the primer?

Bare wood takes one full coat of primer before the enamel, so the primer line reads: 1 coat over 127.57 ft2. Divide that area by the primer label rate to get the primer volume, then round up to the primer container sizes. No primer volume is stated here, because no primer rate is in this source pack and the enamel rate must not be borrowed for it. Keep primer and enamel as separate lines in the order. The paint coats and primer guide shows how the two lines stay separate when only part of a job needs primer.

Three checks that confirm the order

First, the metric check. The rate converts with the same factor: 400 ft2 per gallon equals 37.16 m2 per gallon. Two coats over 11.85 m2 give 23.70 m2, and 23.70 ÷ 37.16 = 0.6379 gallon, matching the imperial figure exactly.

Second, the other-product check. Sherwin-Williams Emerald Urethane Trim Enamel covers 350 to 400 ft2 per gallon. At its low end, the same two coats need 255.15 ÷ 350 = 0.7290 gallon, also under 1 gallon. The 1-gallon order holds for either product. Only the schedule changes: Emerald recoats in 4 hours at 77 °F and 50 percent relative humidity, while Advance needs 16 hours, so its second coat waits until the next day.

Third, the capacity check. One gallon at the low-end rate covers 400 ft2 against 255.15 ft2 needed, leaving 144.85 ft2 of coverage margin for cutting in, edges, and a second pass. If the margin had come out near zero, the order would move up a container even though the exact volume fit.

What changes this answer?

• One door painted on one side only. Remove one slab side, 16.67 ft2, giving 110.91 ft2. Two coats give 221.81 ft2, which is 0.55 gallon at the low end, still 1 gallon.
• Paneled doors. The flat rectangle understates a paneled door, because the recessed panels add faces inside the rectangle. Add the panel faces separately. No panel multiplier is used here, because no source in this pack publishes one.
• Profiled baseboard. A profiled piece has more painted surface than its flat width suggests. Run a flexible tape over the profile to get the developed width, and use the low-end rate.
• A drastic color change. The Emerald data sheet says a primer coat improves hiding when the color change is drastic. That adds a primer line, not extra enamel coats, and the primer still follows its own label rate.
• A different enamel. The container count stays at 1 gallon for Emerald, but the recoat gap and the return-to-service period follow the new label, not the old one.

The general ordering method, including how to draw the cut plan and when to add a spare container, is covered in the trim and door paint ordering guide, and the trim and door paint mistakes guide lists the counting errors that break this kind of math.

Safety and professional scope

Apply Advance between 50 and 100 °F, let each coat dry before recoating, and allow its 7 days to return to service before the surface takes normal hard use. In a home built before 1978, do not sand or scrape old trim or door paint to prepare it without checking for lead first: work that disturbs lead paint in such homes must be done by lead-safe certified contractors. This example plans quantities. It does not select the sheen, set the surface preparation, approve a stain-grade finish, or specify exterior trim. The product labels and the project specification control those decisions.