Calculator

Baseboard & Trim Calculator

Baseboard is bought by the linear foot but sold in fixed board lengths (typically 8, 12, and 16 feet), and the gap between 'linear feet needed' and 'linear feet purchased' is almost entirely down to two things: doorway deductions and miter-cut waste at corners. This calculator starts from room perimeter, subtracts doorway openings, and rounds up to standard stock lengths rather than assuming baseboard comes in exactly the length you need.

Inside and outside corners each get measured and mitered differently, and it's worth reading through before you cut — how to measure a room for baseboard and trim walks through both.

Calculate your quantity

Room length (ft)

Room width (ft)

Doorways

Doorway width (ft)

Board stock length (ft)

Waste factor (%)

Extra for miter cuts and mistakes.

Baseboard boards

7 8ft boards

Linear feet needed: 46 ft
With waste: 50.6 ft

Shopping summary

• 7 x 8ft board(s)

This is an estimate — confirm structural work with a professional.

How this calculation works

Linear footage needed = room perimeter minus the width of each doorway opening (baseboard doesn't run across a doorway threshold). Add a miter-waste allowance — every inside or outside corner requires a 45-degree cut, and cut offcuts from one piece often can't be reused for the next wall's length, so 10% waste on top of net perimeter is a reasonable standard allowance, more on rooms with lots of corners or bump-outs.

Then round up to standard board lengths. If a wall run is 14 feet, you can't buy a 14-foot board — you buy a 16-footer and waste 2 feet, or splice two shorter boards with a scarf joint at a stud location. Planning which wall gets the splice (usually the longest, least-visible run) avoids an obvious seam on a short, high-visibility wall.

The formula

boards = ceil( (perimeter − doors × doorWidth) × (1 + wastePct/100) / boardLength )

perimeter: Room perimeter in feet from length and width, counted once around — baseboard that returns into a closet or alcove needs its own perimeter added into the room dimensions by the person measuring, since this formula only sees one rectangle.
doors × doorWidth: A linear-foot deduction, not a fixed 3 ft assumption like some of this site's other calculators — doorWidth is its own field here, so a 2.5 ft closet door and a 3.5 ft double doorway subtract different amounts even at the same door count.
boardLength: The stock length being bought — 8, 12, or 16 ft — divided into the waste-inflated linear footage AFTER waste is added, so choosing a longer stock length changes the board COUNT even when the underlying linear footage needed is identical.

Where these numbers come from

10% miter-cut waste: Trade convention for a room with ordinary square corners; the field accepts any value, and a room with bump-outs, bays, or many short returns realistically needs a higher figure entered by hand since the formula has no corner-count input to derive it from.
8, 12, and 16 ft stock lengths: Manufacturer-published range of commonly stocked lengths at most home centers; some suppliers also carry 10 and 14 ft, which is exactly why board length is a free-entry field rather than a fixed set of three choices.
boards = ceil(total linear feet / one stock length): This board count assumes every purchased piece is the SAME chosen stock length — the function has no mixed-length optimizer built in. A real order that combines, say, a few 8-footers with a 12-footer to match specific wall runs will typically use fewer total linear feet than this single-length total implies.

Worked examples

A 9 by 11 foot bedroom, one door, 8 ft stock

Inputs
Room length	9 ft
Room width	11 ft
Doorways	1
Doorway width	2.5 ft
Board stock length	8 ft
Waste factor	10 %

Result
Baseboard boards	6 8ft boards
Linear feet needed	37.5 ft
With waste	41.25 ft

40 feet of perimeter minus a 2.5 ft doorway leaves 37.5 linear feet, and 10% miter waste brings that to 41.25 ft — which needs 6 eight-foot boards, or 48 ft of stock against 37.5 ft of actual wall. Nearly 11 feet of that purchase is offcut.

That much offcut on a plain rectangular room is mostly the rounding cost of short stock: four walls rarely divide evenly into 8 ft lengths, so every wall run tends to waste part of its last board even before any miter cut is made.

A 22 by 5 foot mudroom hallway, three doors, 16 ft stock

Inputs
Room length	22 ft
Room width	5 ft
Doorways	3
Doorway width	2.5 ft
Board stock length	16 ft
Waste factor	12 %

Result
Baseboard boards	4 16ft boards
Linear feet needed	46.5 ft
With waste	52.08 ft

This hallway's 54 ft perimeter loses 7.5 ft to three doorways — about one foot in seven — leaving 46.5 net feet, and at 12% waste for the extra cut lines three doorways add, that's 52.08 ft needed. Buying 16 ft stock instead of 8 ft covers it in just 4 boards, 64 ft of stock against 46.5 needed.

Switching from 8 ft to 16 ft stock on a long, door-heavy run like this trades more total offcut (17.5 ft of it here) for fewer physical boards and fewer splice joints — worth it on a run this length, where a splice would otherwise fall in the middle of a highly visible hallway wall.

Common mistakes

Ordering exact linear footage with no corner-waste allowance, which comes up short as soon as the first 45-degree cut is made.
Not planning splice locations ahead of time, resulting in a visible seam on a short prominent wall instead of a long inconspicuous one.
Forgetting closets — closet perimeter still needs baseboard even though it's easy to overlook when eyeballing a room.
Buying random board lengths instead of standardizing on 12 or 16-footers, which increases both waste and the number of splices needed.
Not test-fitting a coped inside-corner joint before committing to the final cut — a coped joint (one board's profile cut to fit over the other) takes practice, and a botched first attempt on the actual stock wastes material that a scrap test cut wouldn't have.
Painting or finishing baseboard before final installation is confirmed, which can complicate touch-ups if a board needs to be re-cut or swapped.

Shopping summary

Buy standard-length boards (8/12/16 ft) totaling at least net perimeter plus 10% miter waste, favoring longer boards on longer wall runs to minimize splices; add matching outside-corner blocks if your trim style uses them instead of mitered corners.

Worked example: a 12x14 room has a perimeter of 52 feet, minus one 3-foot doorway = 49 feet net. Add 10% miter waste: 49 x 1.1 ≈ 54 linear feet. Buying four 12-foot boards (48 ft) and one 8-foot board (8 ft) covers 56 feet with minimal leftover, better matched to the room's actual wall run lengths than trying to buy the bare 54-foot minimum in odd combinations.

FAQ

Do closets count in baseboard footage?

Yes — closet walls need baseboard just like the main room, and it's a common miss since closets are easy to forget when eyeballing perimeter.

Is 10% enough waste allowance for miter cuts?

For a simple rectangular room, yes; rooms with bay windows, multiple closets, or unusual angles often run closer to 15%, since each additional corner adds another cut that can't always reuse the offcut.

What's the difference between a coped joint and a mitered inside corner?

A mitered inside corner joins two 45-degree cuts, similar to an outside corner but pointing inward, and can open up a visible gap if the wall corner isn't exactly 90 degrees; a coped joint cuts one board's profile to fit directly against the face of the other, which tolerates a slightly out-of-square corner better and is generally preferred by trim carpenters for inside corners specifically.

Should baseboard be installed before or after flooring?

Generally after new flooring is installed, so the baseboard sits on top of and covers the flooring's expansion gap at the wall line — installing baseboard first can mean recutting or shimming it once flooring goes in and changes the finished floor height.

What standard board lengths should I plan around when ordering?

8, 12, and 16-foot lengths are the most commonly stocked at home centers, with some suppliers also carrying 10 and 14-foot boards — favoring the longest board that comfortably covers a given wall run minimizes both waste and the number of splices needed across the room.

Do outside corners need extra board length beyond the wall measurement?

Not extra length exactly, but each outside corner uses more of the board per linear foot of wall than an inside corner does, since the 45-degree miter removes material at an angle rather than a straight butt — this is part of why the standard 10% waste allowance exists rather than ordering exact wall-length totals.

Where to go next

The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.