How to use the baseboard and trim calculator
- Pick the trim type (baseboard, crown molding, chair rail or shoe molding) and the unit you measured in.
- Add one row per wall run with its length and the total width of doors or other gaps to subtract. Leave the openings blank for crown molding.
- Enter the inside and outside corners, keep the 2 inch extra length for each run, and choose a board length or leave it on Best fit.
- Read the boards to buy, the feet bought and left over, and the table that compares 8, 10, 12 and 16 foot boards. Copy the shopping list.
Formula
Run length = wall length - openings on that wall
Cut length = run length x 12 + extra inches
A run longer than a board is split into whole boards and one shorter piece
Boards = all pieces packed into board lengths, longest first
Boards to buy = packed boards x (1 + waste percent / 100), rounded up
Feet bought = boards to buy x board length
Left over = feet bought - total cut length
Packing means a short run can share a board with the leftover of another run. The tool tries each board length and picks the one that buys the fewest feet, and the fewest boards if two lengths tie. Waste is applied to the board count after packing.
Worked example: baseboard for a 12 by 10 foot room with two doors
The walls are 12, 10, 12 and 10 feet. A 3 foot door on the first wall and another on the last leave runs of 9, 10, 12 and 7 feet, which is 38 feet of baseboard.
With 2 inches extra on each run the cut lengths are 110, 122, 146 and 86 inches, or 38.67 ft in all.
With 5% extra boards, 8 foot boards win: the pieces pack into 5 boards and 6 are bought, which is 48 feet with 9.3 feet left over. Ten foot boards need 5 and buy 50 feet, and twelve foot boards need 5 and buy 60 feet.
With no extra boards, 8 ft and 10 ft boards both buy 40 feet, and the tool picks four 10 ft boards because it is fewer pieces to handle.
Why board length matters
Trim comes in set lengths, and the best choice depends on how your walls divide into those lengths. A room with a few long walls can use long boards with little waste, while a room with many short runs, such as a hallway or a closet, wastes less with 8 foot boards. The comparison table shows how each length performs on your own walls instead of using a flat percentage.
Longer boards are harder to carry and can arrive bowed. Many pros still prefer them for long walls because a single piece means fewer joints. If a run is longer than your board, the tool splits it and counts a splice, which should be cut at an angle and placed where it will be least visible.
Corners, doors and extra length
Inside corners are joined by coping one board to fit the face of the other, or by a mitered cut, and outside corners are mitered. Either method uses a little extra length, which is why each run gets a few inches of allowance. The corner counts are shown in the shopping list so you can plan the cuts.
Baseboard stops at doorways, so subtract the door width from the wall it is on. For crown molding and chair rail you normally run past doors, so leave the openings blank. Trim also stops at built-ins, fireplaces and cabinets, and you can enter those widths as openings too.
Buying and finishing
Buy all the trim for a room at once and let it sit in the room for a day or two so it adjusts to the air. Prefinished trim saves painting time, but every cut end needs touch-up. Caulk, nails, adhesive, filler, primer and paint are not included, and neither are door casings and window trim unless you list them as wall runs.
Assumptions and limits
- Each wall is a single straight run. Bay windows, angled walls and curved walls need their own rows with measured lengths.
- The 2 inch extra length is an example allowance for miters and trimming. Increase it for complex corners.
- Boards come in the lengths shown. Your store may stock different lengths, so use the stock option that matches.
- Waste is added to the packed board count, and a bad cut on a long board costs a whole board.
- Profiles with a repeating pattern, scarf joints and special corner blocks are not modeled.
Frequently asked questions
How do I calculate how much baseboard I need?
Add up the length of every wall, subtract the width of door openings, and add a few inches for each run. Then divide into board lengths, remembering that short leftovers can be reused.
Should I subtract doors when measuring crown molding?
No. Crown molding runs across the top of the wall above doors, so use the full wall length. Baseboard and shoe molding stop at the door, so subtract the width.
Is it better to buy 8 foot or 16 foot trim boards?
It depends on your walls. Long boards reduce joints on long walls, and short boards waste less on short runs. The comparison table shows the feet bought for each length.
How many corners does a room have?
A plain rectangular room has 4 inside corners. Each projecting wall, column or chimney breast adds outside corners, so count them on your floor plan.
Why does the tool add extra inches to every run?
Cuts at corners are angled, so the board needs to be a little longer than the wall. The extra length also gives room to trim a piece to a tight fit.