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Linear Feet Calculator

Linear feet from room size, and how many lengths that is.

Your measurementsEvery assumption editable01

Doorways and other gaps with no material across them.

Linear runCalculated live02

Result

50linear ft

50 ft — 7 × 8 ft lengths

Perimeter2 × (16 + 12)
56 ft
Less openings
−6 ft
Net run
50 ft
With waste+10%
55 ft
Lengths to buy
7 × 8 ft

Linear feet measures length alone, with width and thickness irrelevant. It is how trim, moulding, pipe, cable and dimensional lumber are sold, and it is not interchangeable with square feet or board feet.

Check your longest single wall before choosing a length to buy. A twelve foot wall needs a twelve foot piece or it shows a joint, and no quantity of eight foot stock fixes that.

For a room that is not a simple rectangle, add the wall lengths individually rather than using the perimeter formula.

Linear feet measures length alone — width and thickness are irrelevant. It is how trim, pipe, cable and dimensional lumber are sold, and it is not interchangeable with square feet or board feet.

Why use this tool?What it does differently03

Why use this tool?

Perimeter handled

From room dimensions, with openings deducted.

Converted to pieces

Material is sold in fixed lengths, so the run becomes a count of what to buy.

Waste included

Mitres and offcuts, adjustable for how many corners the job has.

Longest wall warning

A twelve foot wall needs a twelve foot length or it shows a joint.

How this worksThe method04

How this linear feet calculator works

Perimeter is twice the sum of length and width. Openings with no material running across them are deducted, the waste allowance is applied, and the result divides by the length you are buying.

Linear feet is a measure of length only. A linear foot of quarter-round and a linear foot of crown moulding are both one foot, despite one being a fraction of the other's volume — which is why it is not interchangeable with board feet.

The waste allowance covers mitres. Each forty-five degree cut leaves an offcut rarely usable at the next corner, so a room with many corners eats more than its perimeter suggests.

How to use itStep by step05

How to use it

  1. Step 1: Measure the room

    Length and width. For non-rectangular rooms, add the wall lengths individually instead.

  2. Step 2: Deduct the openings

    Total width of doorways and gaps with no material across them.

  3. Step 3: Note your longest wall

    Before choosing a length to buy — it determines whether you can avoid a joint.

  4. Step 4: Set the waste

    10% for a simple room, more for many corners or a first attempt at mitres.

Example usageWorked figures06

Example usage

A standard room
16 by 12 ft has a 56 ft perimeter. Less 6 ft of doorways is 50 ft, 55 with waste — seven 8 ft lengths.
Buying longer stock
The same room in 16 ft lengths needs four pieces. Same footage, far fewer joints on the long walls.
A corridor
A 30 by 4 ft hallway has a 68 ft perimeter despite only 120 sq ft of floor. Long thin rooms are trim-heavy relative to their area.
Frequently asked questionsCommon questions07

Frequently asked questions

What is a linear foot?

One foot of length, regardless of width or thickness. It is how trim, pipe, cable and dimensional lumber are sold.

How is linear feet different from square feet?

Linear measures length only; square measures area. A linear foot of six inch board and a linear foot of twelve inch board are both one linear foot but different square footage.

How is it different from board feet?

Board feet is a volume, accounting for thickness and width. Two pieces with identical linear footage can have very different board footage.

How much waste should I allow for trim?

Ten per cent for a simple room. More where there are many corners, since each mitre leaves an offcut that rarely fits the next corner.

What length should I buy?

Long enough to run your longest wall in one piece. A joint mid-wall is visible however carefully it is scarfed.

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