How do I find the perimeter?

Measure along the base of every wall and add them up. For a simple rectangular room it's 2 × (length + width); for an L-shaped or bumped-out room, total each wall segment individually.

Should I subtract doorways?

Yes — cased openings and doorways get no baseboard, so subtract their total width. Don't subtract windows; baseboard runs underneath them. The calculator's “openings” field is for doorways and similar gaps. (Crown molding is different — it runs at the ceiling and breaks at neither doors nor windows, so set openings to 0 for crown.)

Why round up to whole pieces?

Trim is sold in fixed lengths, so you buy whole boards and cut to fit. Buying by the piece also lets you plan where the joints fall — longer stock means fewer seams on long walls. Keep an offcut for future repairs.

Baseboard Calculator

Enter the room's perimeter and the openings to skip, and this gives the linear feet of baseboard — and the number of stock pieces — to buy.

Baseboard needed

37.4linear ft

Stock pieces: 5 pieces
Wall to cover: 34 linear ft

How these numbers are worked out

The formula

Wall to cover = perimeter − openings (doorways get no baseboard). Linear feet to buy = that × (1 + waste), since miter cuts and offcuts waste a little at each corner. Pieces = linear feet ÷ stock length, rounded up. A chair rail uses the same math (it also breaks at doors and runs under windows). Crown molding is the exception — it runs at the ceiling, so it breaks at neither doors nor windows: set openings to 0 for crown.

Constants and sources

Linear feet = (perimeter − openings) × (1 + waste); pieces = linear feet ÷ stock length, rounded up. Geometry.

How it was checked

Last reviewed June 16, 2026. Before this calculator was published, its formula, constants and worked example were checked in a separate, AI-assisted review that redid the arithmetic and tested the factual claims; the site owner then approved it for publishing. No engineer or tradesperson reviews these pages. Where a figure depends on the product (a density, a coverage rate, a bag size), it is either an input you can change above or a fixed planning value stated on this page, so check it against your product's label or your supplier.

Spot a wrong number or an outdated figure? Send a correction.

Worked example

A room with a 40-ft perimeter and 6 ft of door openings: 40 − 6 = 34 ft to cover; × 1.10 = 37.4 linear ft; ⌈37.4 ÷ 8⌉ = 5 eight-foot pieces.

FAQs

How do I find the perimeter?: Measure along the base of every wall and add them up. For a simple rectangular room it's 2 × (length + width); for an L-shaped or bumped-out room, total each wall segment individually.
Should I subtract doorways?: Yes — cased openings and doorways get no baseboard, so subtract their total width. Don't subtract windows; baseboard runs underneath them. The calculator's “openings” field is for doorways and similar gaps. (Crown molding is different — it runs at the ceiling and breaks at neither doors nor windows, so set openings to 0 for crown.)
Why round up to whole pieces?: Trim is sold in fixed lengths, so you buy whole boards and cut to fit. Buying by the piece also lets you plan where the joints fall — longer stock means fewer seams on long walls. Keep an offcut for future repairs.