Trim calculator

Baseboard, crown, and door and window casing in linear feet and sticks — with baseboard deducting the doorways, crown running the full perimeter, and casing counted per opening and per face. Imperial or metric.

01 How the math works

Every trim run starts from the room perimeter — twice the length plus twice the width. What changes between profiles is which openings you subtract. Baseboard runs along the floor and stops at each side of a doorway, so it is the perimeter less the sum of the door opening widths. Crown runs along the ceiling and passes over the top of every doorway, so it takes the full perimeter with nothing deducted. Casing is different again: it is not a perimeter number at all but a per-opening figure — two legs up the jamb plus a head across the top.

An interior door is cased on both faces of the wall, so its casing run is doubled — a door counts 2 × height + width on each side. A window is cased on one face and picture-framed on four sides, so it counts 2 × height + 2 × width. Because baseboard, casing, and crown are usually different profiles, each is ordered as its own run of sticks at the stock length you carry.

02 Worked example

Take a 12 ft × 14 ft bedroom (3.66 m × 4.27 m) with one 36 in (914 mm) door opening and one 36 × 48 in (914 × 1,219 mm) window — the single-room hang from our drywall and paint examples, now trimmed out.

The perimeter is 2 × (12 + 14) = 52 lin ft (15.85 m). Baseboard subtracts the one 3 ft door opening: 52 − 3 = 49 lin ft (14.94 m). Crown takes the full 52 lin ft (15.85 m) — it runs over the doorway, not around it. That 3 ft gap is exactly the doorway, and it is where single-perimeter calculators go wrong in one direction or the other.

Door casing is one interior door on both faces: 2 × 80 + 36 = 196 in per face, 392 in = 32.67 lin ft (9.96 m). Case it on one side only and you order half. Window casing, four-sided on one face, is 2 × 48 + 2 × 36 = 168 in = 14 lin ft (4.27 m). At 16 ft stock with 10% waste that rounds to 4 sticks of base, 4 of crown, and 4 of casing.

03 When this calculator is wrong

The result is a clean-rectangle takeoff. Real trim work bends that in a few specific ways, and the miters are where the linear feet turn into ordered length.

• Buy long, cut short — miters eat the ends. Every inside and outside corner is a mitered cut, and a bad miter is a wasted end, not a wasted inch. The price-per-foot premium on 16 ft trim over 8 ft is usually under 15%, but the longer stock means fewer splices in the middle of a wall, where a joint always shows. The exception is transport: a 16 ft stick doesn't fit in a hatchback, and a room of short walls may run better on 8 ft stock.
• It assumes one door and window size. The calculator applies the single door and window dimensions you enter to every opening of that type. A room with a 36 in door and a 60 in patio slider needs the two run separately and added — the head and legs differ on each.
• The door deduction is the cased opening, not the slab. Baseboard stops at the door casing, not at the door itself, so the true gap is the opening width plus the two casing widths. On a 36 in door with 2-1/4 in casing that is about 4.5 in (114 mm) more per door — small on one door, worth a stick on a whole floor of them.
• Windows aren't always four-sided. A stool-and-apron window is cased on three sides — two legs and a head — with a stool and apron below instead of a fourth casing leg. If that's your detail, the window casing figure above runs slightly long. Pre-finished stools and aprons are ordered as their own pieces.

04 What to do with the result

Order each profile as its own run at the longest stock length that fits the room, then round up to whole sticks — trim is sold by the piece, and half a stick short means a return trip for a matched profile that may not be on the shelf. Keep the waste factor at 10% for a plain rectangular room; step it toward 15% when the room has many corners, since each outside corner is a two-miter cut with an offcut on both sides. Take the casing count as sticks, but confirm your door count and whether each door is cased one face or two before you commit — that single choice moves the door casing number the most.

05 Common questions

How do I calculate how much baseboard I need?

Measure the room perimeter — twice the length plus twice the width — and subtract each door opening, since baseboard stops at the doorway. For a 12 × 14 ft room with one 3 ft door that is 52 − 3 = 49 lin ft. Add a waste factor and round up to whole sticks at your stock length.

Is crown molding the same length as baseboard?

No. Crown runs along the ceiling and passes over the top of every doorway, so it takes the full perimeter with no door deduction. Baseboard runs along the floor and stops at each door. In the example above, crown is 52 lin ft and baseboard is 49 lin ft — the difference is the doorway.

How much casing does one door need?

One face of a standard 6'8" (80 in) door with a 36 in opening needs 2 × 80 + 36 = 196 in, about 16.3 lin ft. An interior door is cased on both faces, so it needs roughly 32.7 lin ft — twice that. Pre-cut casing sets are sold to case a single 6'8" opening on one face.

Why does the door casing count both sides?

Because you see both sides. An interior wall opening is trimmed on each face, so the casing run is doubled. A closet or an opening cased on one side only takes the single-face number — change the door faces from two to one for that case.

What waste factor should I use for trim?

10% covers a plain rectangular room. Step toward 15% when the room is cut up with many corners: each outside corner is a two-miter joint that wastes an end on both meeting pieces, and complex rooms accumulate those cuts fast.