How to use the baseboard and trim calculator
Interior trim is bought by the length, but it is used in short runs between corners, doors and windows, so a quick perimeter figure rarely matches what you actually order. This calculator separates the four common trims, baseboard, door casing, window casing and crown molding, works out the net length of each, adds a waste allowance and converts the result into stock lengths.
- Choose units. US mode takes the room in feet and the openings in inches. Metric mode takes metres and millimetres, so you can work in skirting, architrave and coving.
- Enter the room as length and width, or switch to a known perimeter for an irregular room. Add up every wall that gets trim, including the short returns in bays and alcoves.
- Enter the doors and windows, their size and the casing width. Choose whether each door is cased on one side or both.
- Set the waste, stock length and price, and whether the room gets crown molding.
Trim formulas
Baseboard = perimeter − doors × door width
Door casing per face = 2 × (door height + casing width) + (door width + 2 × casing width)
Window casing = 2 × (window width + 2 × casing width) + 2 × (window height + 2 × casing width)
Crown molding = perimeter
Lengths to buy = ⌈net length × (1 + waste %) ÷ stock length⌉
The casing formulas include the extra length that the mitred corners need, measured on the outside edge of the trim. The stock count is a total for each trim type; a cut list per wall can come out one piece higher when walls are just longer than a stock length.
| Trim | US term | UK term | Typical stock lengths |
|---|---|---|---|
| Wall base | Baseboard | Skirting board | 8, 12, 16 ft · 2.4, 3.0, 4.2 m |
| Door and window frame | Casing | Architrave | 7, 14 ft · 2.1, 2.4 m |
| Wall to ceiling | Crown molding | Coving, cornice | 8, 12, 16 ft · 2.0, 3.0 m |
| Mid-wall | Chair rail | Dado rail | 8, 16 ft · 2.4, 3.0 m |
A chair rail or picture rail follows the perimeter less door widths, so you can price one by running the baseboard line again.
Worked examples
A 12 × 14 ft bedroom
The perimeter is 52 ft. With one 36 in door, the baseboard is 49 ft, or 53.9 ft with 10% waste: four 16 ft lengths. Casing one face of the 36 × 80 in door with 2½ in casing takes about 17.2 ft, so two 16 ft lengths with waste. Two 36 × 48 in windows take about 15.7 ft each, 31.3 ft in total, so three lengths. Crown molding around the full 52 ft is 57.2 ft with waste, or four lengths. That is about 150 ft of trim before waste and 164 ft after it.
A 4 × 3.5 m living room
The perimeter is 15 m. With one 900 mm door, the skirting is 14.1 m, or 15.5 m with 10% waste, so seven 2.4 m lengths. Casing both sides of the 900 × 2,100 mm door with 70 mm architrave takes 5.38 m per face, or 10.76 m in total, which is 11.8 m with waste and five 2.4 m lengths.
Who this calculator helps
- Interior designers and architects scheduling trims for a finishes specification or cost plan.
- Finish carpenters and joiners putting together a materials list for a quote.
- Renovation contractors pricing new skirting and architrave across a whole house.
- Homeowners buying trim for a DIY room refresh in one trip.
Practical tips
- Buy the longest lengths you can transport, so long walls need no joins; join with a scarf cut over a stud where you must.
- Cope inside corners on profiled baseboard and crown; it hides seasonal movement better than a straight mitre.
- Prime and paint trim before fitting and touch up after; the paint calculator covers the walls, and trim usually needs about one litre or a quart per room.
- Convert awkward site measurements with the feet and inches converter, and get board areas for walls from the drywall calculator.
Want to compare a Shaker baseboard with a period profile before ordering? Show the client the restyled room on a photo with Room Redesign.
