Baseboard and Trim Calculator

Work out linear feet of baseboard for a room and how many stock lengths to buy.

Draft — figures checked, awaiting an editorial read. Not indexed.

Formula: Perimeter = 2 × (length + width), minus doorway widths. Pieces = perimeter × (1 + waste) ÷ stock length.

What this calculates

This works out how much baseboard, shoe moulding or crown a room needs, and converts it into whole stock lengths — which is what you actually buy. Trim is one of the few materials where buying long boards is meaningfully better than buying the exact footage: every joint in a run is visible, and a wall you can cover with one continuous piece will always look better than the same wall covered with two pieces and a scarf joint, even a well-cut one.

How it works

The room perimeter is twice the length plus twice the width. Doorway widths are subtracted, since no baseboard runs across an opening. The waste allowance is then applied and the result divided by your stock length, rounded up. Ten percent is the sensible minimum for waste here because every inside corner is either coped or mitred, and both operations consume material and produce the occasional ruined cut. Rooms with bay windows, chimney breasts or angled walls should go higher.

Worked example

A 14 by 12 foot room with two 32 inch doorways, using 16 foot stock. Perimeter: 2 × (14 + 12) = 52 feet. Doorways: 2 × (32 ÷ 12) = 5.3 feet, leaving 46.7 feet of baseboard. Add 10% waste for 51.4 feet, divide by 16 and you need 4 pieces — 64 feet of stock. The apparent excess is not waste; it is what lets you cut each wall from a single length rather than joining mid-run.

Common mistakes

Buying exactly the calculated footage in the shortest stock available. It costs less and looks worse, permanently. Second, forgetting that inside corners on baseboard are normally coped rather than mitred — coping takes longer and eats an extra inch or two per corner, and it is worth doing because coped joints stay tight when the house moves. Third, subtracting doorway widths and then forgetting to add back the trim that returns into the door casing.

Common questions

How much extra baseboard should I buy?

At least 10%, and take whole long lengths rather than the exact footage. Being able to run a wall in one uninterrupted piece is worth more than the small saving on offcuts.

Should I mitre or cope inside corners?

Cope them. Mitred inside corners open into a visible gap as the house moves seasonally; a coped joint stays closed because one piece is scribed to the profile of the other.