Trim & Baseboard Calculator
Work out the baseboard, casing and crown a room needs, in whole lengths. A real cutting list reuses offcuts, so you buy boards instead of guessing from linear feet.
How to Use
- Enter the room length and width.
- Enter the number of doors and their opening width, and the windows with their width and height.
- Enter the casing width; it adds the mitre length to each casing piece.
- Choose the stock length you can buy, tick crown if you are adding it, and set a spare allowance for mistakes.
- Read how many lengths of each to buy; the cutting list shows which piece comes from which board.
Worked Example
A 12 × 14 ft bedroom with one 36 in doorway and two 36 × 48 in windows, 2¼ in casing, 16 ft stock. Baseboard: the perimeter is 52 ft, less 3 ft for the door, 49 ft. The door splits one 14 ft wall into two 5 ft 6 in runs, so the runs are 14, 12, 12, 5½ and 5½ ft. Longest first: 14 ft on board 1, 12 ft on board 2, 12 ft on board 3, and both 5½ ft runs on board 4. 4 lengths, plus 10% spare, so buy 5.
Casing: the door takes two legs of 80 + 2¼ = 82¼ in and a head of 36 + 4½ = 40½ in. Each window takes two sides of 52½ in and a top and bottom of 40½ in. Those 11 pieces, 48 ft in all, pack into 4 lengths of 16 ft: the two door legs on one, three 52½ in sides on the next, and so on.
The common mistake: dividing the total by the board length. 49 ft ÷ 16 = 3.1, so 4 boards, which happens to match here. In an 11 × 11 ft room on 16 ft stock, the same sum says 44 ÷ 16 = 2.75, so 3 boards, but every 11 ft wall needs its own board unless you add joints, so it takes 4.
Show Work
Formulas
Copes, Mitres and Cutting Lists
Baseboard began as a practical strip to protect plaster from mops and boots and to hide the gap where the wall meets the floor. Finish carpenters join it with a cope at inside corners, cutting the profile of one piece to fit over the face of the other, because a cope stays tight when the wall moves and a mitre opens up. Outside corners and casings are mitred.
Working out which pieces to cut from which board is the cutting stock problem, studied by Leonid Kantorovich in 1939 and one of the first problems tackled with linear programming. For a room’s worth of trim, packing the longest pieces first and filling each board with the next piece that fits gets the optimum or within a board of it.
About This Calculator
This calculator works out the baseboard, door and window casing and crown moulding for a rectangular room and turns them into a cutting list on the stock length you choose, reusing offcuts and counting the whole lengths to buy, in feet or metres. Each door is placed on the wall with the most clear length left.
Everything runs in your browser; nothing is sent anywhere. Casing is counted for the room side of each door only; add the same again for the other side. Saw kerfs are not deducted, so leave a little in hand on tightly packed boards.
Related calculators: Flooring Calculator, Paint Calculator, and Drywall Calculator.
Frequently Asked Questions
How do I measure for baseboard?
Measure the perimeter of the room and subtract the doorways, measured to the outside of the casing. A 12 × 14 ft room is 52 ft around; with one 36 in doorway, 49 ft of baseboard. Buy whole lengths, planning each wall so that it is one piece where possible.
How much trim do I need for a door?
One side of a standard 80 in door takes two side legs of about 82¼ in and a head the width of the opening plus two casing widths, about 17 ft in all. The other side of the door needs the same again. Pre-cut 7 ft casing sets are sold for exactly this.
How much casing for a window?
Picture-framed, all four sides: twice the height plus twice the width, each plus two casing widths for the mitres. A 36 × 48 in window with 2¼ in casing takes 2 × 52.5 + 2 × 40.5 = 186 in, about 15½ ft. Windows with a stool and apron use a little more at the bottom.
Why not just divide the linear feet by the board length?
Because pieces cannot be joined anywhere. An 11 ft wall uses most of a 16 ft board, and the 5 ft offcut is only useful for a run of 5 ft or less. The cutting list packs the actual pieces, longest first, into boards, which gives the true count: an 11 × 11 ft room is 44 ft, which divides into 2.75 boards, but needs 4 without joints.
How much extra trim should I buy?
About 10%, or one spare length per ten. Mitres and copes take practice and a bad cut wastes a whole piece if it was cut to fit. Returning an unused length is easier than a trip back in the middle of a job.
How do I use the Trim & Baseboard Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Bedroom
12×14 ft, one door, two windows: 4 lengths of baseboard and 4 of casing, plus one spare each.
Living room with crown
16×20 ft, two doors, three windows: baseboard, casing and 72 ft of crown on 16 ft lengths.
Hallway
4×20 ft with four doors on 12 ft stock: the cut list reuses the offcuts between doors.
Metric room
3.6 × 4.2 m with one door and a window, on 2.4 m lengths.
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