Trim Calculator
Baseboard, crown moulding or door and window casing: the length you need, a cut plan from your stock length, the pieces to buy and the cost.
Result…
How it's calculated
Baseboard length = perimeter − doorway widths (or the sum of the wall runs) Crown length = perimeter Casing per opening = 2 × (height + casing width) + (width + 2 × casing width); 4 sides: 2 × (height + 2 × casing width) + 2 × (width + 2 × casing width) Pieces (cut plan) = cuts packed into stock lengths, longest first Pieces (with extra) = length × (1 + waste %) ÷ stock length, rounded up Buy = the larger of the two
Works out how much baseboard (skirting), crown moulding or door and window casing to buy. Baseboard is the room perimeter less the doorways, crown is the whole perimeter, and casing is two sides and a head (or four sides for a picture-framed window) measured to the long point of the mitres. Runs longer than one stock length are joined, and the calculator packs every cut into whole stock lengths, longest first, to show how many pieces the job really needs and which cuts come from each piece. It also adds your waste allowance to the total length, and you buy whichever count is larger. Stock lengths and prices differ by supplier and country, so you enter them.
Your numbers, step by step
About the Trim calculator
This trim calculator works out how much baseboard (skirting), crown moulding or door and window casing to buy, and how many pieces of your stock length that takes. Enter the room length and width, or each wall run, and for baseboard the doorways to leave out. For casing, enter the openings and the casing width, and it measures each side to the long point of the mitres. Runs longer than one piece are joined, with no tiny splice pieces, and every cut is packed into whole stock lengths, longest first. You see which cuts come from each piece, the joints, the offcuts left over and the cost if you add a price per piece. Your waste allowance is checked against the cut plan, and you buy whichever count is larger. Stock lengths differ by supplier, so you enter yours, in metres or feet.
How to use it
- Choose metric or imperial units, then pick “Baseboard”, “Crown” or “Casing” under “Trim”.
- For baseboard or crown, enter the “Room length” and “Room width”, or switch “Measure by” to “Wall lengths” and type each run.
- For baseboard, enter the “Doorways” and the “Doorway width”; for casing, enter the openings, their size, the “Casing width” and the “Cased sides”.
- Enter the “Stock length” your supplier sells and an “Extra for waste” for mitres, coping and mistakes.
- Add a “Price per piece (optional)”, then read the pieces to buy and the cut plan in the steps.
Worked example
Baseboard for a 4.5 × 3.6 m room with one 0.9 m doorway, from 2.4 m lengths. The perimeter is 2 × (4.5 + 3.6) = 16.2 m, less 0.9 m for the doorway = 15.3 m. Each wall is longer than 2.4 m, so each gets a joint, and the 8 cuts pack into 7 pieces. With 10% extra, 15.3 × 1.1 = 16.83 m ÷ 2.4 = 7.01, rounded up to 8. Buy 8 pieces, which leaves 3.9 m of offcuts. At 8 per piece the trim costs 64.
Updated
Questions people ask
How do I calculate how much baseboard I need?
Add up the lengths of the walls (2 × length + 2 × width for a rectangular room) and take off the width of each doorway. Divide by the stock length, add an allowance for waste and round up to whole pieces.
How much extra trim should I buy for waste?
It depends on how many corners you cut and how practised you are. Mitred and coped corners and short returns use more, so enter your own allowance; the calculator also builds a cut plan and buys the larger of the two counts.
How do I work out the length of door casing?
Each side runs the height of the opening plus one casing width to the long point of the mitre, and the head runs the width plus two casing widths. A window cased on four sides adds a bottom piece and two casing widths to each side.
Why does the cut plan need more pieces than the total length suggests?
Cuts can't be joined from scraps without a visible joint, so a 2.1 m cut needs a fresh piece even if two 1.2 m offcuts are lying around. Packing the real cuts into whole lengths shows the true count.
Does crown moulding need less for doorways?
No. Crown runs round the whole ceiling, so it uses the full perimeter; only baseboard stops at doorways. For the floor or wall area of the same room, use the square footage calculator or the paint calculator.
What doesn't this trim estimate include?
It ignores the saw kerf, the reveal on casing and walls that are out of square, all of which the waste allowance should cover. Check the stock lengths and profiles your supplier actually has before you buy.