Linear Feet to Square Feet Calculator

LF ↔ SF Conversion Calculator

Pick the direction you need, enter the material's actual width, and read the answer with the waste factor already applied. Width is what makes the conversion possible — a linear foot alone carries no area information.

Linear Feet vs Square Feet: Two Different Dimensions

The linear feet vs square feet confusion comes down to dimensions: one versus two. What's a linear foot? It is exactly 12 inches of length measured along a single line — no width, no thickness, no area. Run a tape measure down the edge of a board and the number you read is linear feet. Square feet, by contrast, measure a surface: length × width. A deck floor, a wall, and a sheet of plywood are all measured in square feet because they have two dimensions that both matter.

The same board can honestly be described both ways. A 12-foot 1x6 trim board is 12 linear feet long. Laid flat, it covers 12 × (5.5 ÷ 12) = 5.5 square feet of surface. The lumberyard sells it as 12 linear feet; the painter priming it cares about the 5.5 square feet of face. Neither number is wrong — they answer different questions. Linear feet answer "how long is the run?" Square feet answer "how much area does it cover?"

This double vocabulary is why decking, siding, fencing, and trim orders go wrong so often. Decking is sold by the linear foot but installed over an area quoted in square feet. The bridge between the two is always board width — and that is the one number a linear-foot price tag never tells you. Once you know the actual width of your material, every conversion on this page becomes a two-step multiplication.

Lineal foot vs linear foot — same unit, different spelling

If you see "lineal foot" on a lumberyard invoice or a fencing quote, it is not a different unit — "lineal" is an older spelling of "linear" that survives throughout the building trades, especially on board tags, delivery tickets, and in older trade catalogs. Both spellings mean exactly the same thing: 12 inches of length, width not included. (The variant also appears in the fixed legal phrase "lineal descendant," which is where it is most at home in general English.) For material orders, treat linear foot, lineal foot, and LF as perfect synonyms. The math never changes: whatever the spelling on the ticket, the yard is measuring the length of your run — and you will still need a width to turn that length into square feet.

The Conversion Formula (and Why Width Is Required)

Both conversions are two-step arithmetic once a width is on the table. To turn linear feet into square feet: SF = LF × width(in) ÷ 12. To turn square feet into linear feet: LF = SF × 12 ÷ width(in). The 12s appear because width is measured in inches while length is measured in feet — dividing by 12 converts inches of width into feet of width so the units cancel cleanly.

The special case worth memorizing: material that is truly 12 inches wide makes the conversion collapse. With 12"-wide material, LF = SF and SF = LF — one linear foot covers exactly one square foot. That is why ordering 12" boards feels so much easier than ordering decking. At the other common extreme, 5.5"-wide decking takes 2.18 linear feet per square foot, and a 3.5"-wide board takes 3.43 lf per square foot — nearly three and a half feet of board for every square foot of wall.

Why is width required? Because linear feet contain no width information at all, there is literally no way to convert LF to SF — or back — without supplying a width from somewhere. One hundred linear feet could be 8.33 sq ft of 1-inch material or 100 sq ft of 12-inch material. Any converter that asks only for linear feet and returns square feet is silently guessing the width for you, and that guess is where orders go wrong. The calculator at the top of this page makes the width an explicit input so the assumption is never hidden.

The 5-Step Conversion SOP

Work any linear-to-square order through these five steps in order. Tick each step off as you complete it — the progress bar tracks how far along your order is.

Common Material Width Chart

Every row below uses the actual dressed width, not the nominal name, so the numbers are safe to order from. LF per 100 sq ft = 100 × 12 ÷ width — so 5.5" decking needs 218 lf per 100 sq ft, 7.25" boards need 166 lf, and true 12" material needs exactly 100 lf. Boards per 100 sq ft assumes 12' stock: each 12' board covers its own width in square feet (a 12' 5.5" board covers 5.5 sq ft).

* For lap siding, "exposure" is the visible face per course, not the board's full width. A 1x8 (7.25" wide) laid with 6" exposure still covers area at the 6" rate: 200 lf per 100 sq ft. See the Don't card below.

Worked Example: Ordering Decking by the Square Foot

Say your deck plan reads 400 square feet and you are buying 5/4x6 pressure-treated decking, whose actual dressed width is 5.5 inches. You need the sqft to linear ft conversion, then a board count. Here is the full order math from blank page to lumberyard ticket.

How many linear feet in a square foot of 5/4x6?

First the per-unit rate: 12 ÷ 5.5 = 2.18 linear feet per square foot. Every square foot of deck surface consumes 2.18 lf of board. That is the number to memorize for 5/4x6 — it works forward and backward for any deck size. (For contrast, a 12"-wide board needs just 1.00 lf per square foot, and a 3.5" deck board needs 3.43.)

Doing the sqft to linear ft math on a real order

Now the order: 400 sq ft × 12 ÷ 5.5 = 872.7 linear feet of decking. Add a 10% waste factor for a typical mixed-length layout: 872.7 × 1.10 = ≈ 960 lf. At 12' stock, 960 ÷ 12 = 80 boards — order 81 to cover defects and mis-cuts. Sanity-check with one board: 80 boards × 5.5 sq ft each = 440 sq ft of coverage, which matches your 400 sq ft plus 10% exactly.

Two related tools keep the rest of the framing budget honest. If you are pricing thick hardwood or comparing lumber sold by volume, the board feet calculator converts between board feet, linear feet, and square feet for dimensional lumber. And if the deck project includes an attached pergola, the pergola rafter calculator sizes those rafters and tells you how many linear feet of framing stock to add to the same lumber order.

The same three moves work for any material: divide 12 by the actual width to get lf per square foot, multiply by area to get total lf, then divide by stock length to get board count. Change only the width and the same pipeline prices a fence, a wall of siding, or a shiplap accent wall.

How to Measure Linear Feet

How do you measure linear feet? Hook a tape measure at one end of the run and read the length at the other — that single number is your linear footage. How to figure linear feet for a whole project is just repetition: measure each straight segment, then add the segments together. Fences and trim are measured by run length — each fence line from corner to corner, each baseboard wall from corner to corner, adding door and gate openings where the material continues through them. Rooms measured for baseboard or crown go by perimeter: a 14' × 12' bedroom has a perimeter of 2 × (14 + 12) = 52 linear feet of wall run, minus door widths if the trim stops at casings.

Three habits keep the number honest. First, measure the actual surface the material covers, not the drawing — framing is rarely perfectly square, and a bowed wall adds real footage. Second, measure in one unit and stay in it; mixing a 15'6" field measurement with decimal entries is where transcription errors live. Third, write each segment down separately so a mistake in one run doesn't contaminate the total.

Figuring linear feet from square feet

The reverse conversion — figuring linear feet from square feet — runs the formula backward: LF = SF × 12 ÷ width. A 220 sq ft wall sided with 7.25"-wide 1x8 needs 220 × 12 ÷ 7.25 = 364 lf of siding coverage. The width is always the actual width or the exposure, whichever controls the layout, and the waste factor applies after the total is summed — never wall by wall, or you double-count the cushion.

How long is a linear foot?

Exactly 12 inches of length — regardless of width, thickness, or material. A linear foot of rope, a linear foot of countertop edge, and a linear foot of 2x12 are all the same 12 inches along the line. Width and thickness change how much a linear foot covers or weighs, but never how long it is. That is why "linear" is in the name: it is a measurement of a line, pure length, one dimension only.

Pricing: How Much Is a Linear Foot?

A linear foot is a pricing unit, so "how much is a linear foot" depends entirely on the material. Decking illustrates the three systems that collide at the lumberyard. 5/4x6 decking might cost $3.20 per linear foot. Because each square foot of deck consumes 2.18 lf of 5.5" board, that same deck costs $3.20 × 2.18 = $6.98 per square foot — and a 400 sq ft deck works out to 872.7 lf × $3.20 = $2,793 before waste, or about 960 lf × $3.20 = $3,072 with a 10% cushion. Quotes per square foot and quotes per linear foot describe the same money; only the multiplication differs.

To compare quotes fairly, convert both to dollars per square foot: take the $/lf price, multiply by 12 ÷ actual width, and you have $/sf. A $2.80/lf quote on 5.5" material is $6.11/sf — cheaper per covered area than a $3.20/lf quote on 3.5" material, which is $10.97/sf. Per-unit prices hide width; per-area prices expose it.

Fencing shows where linear-foot pricing genuinely belongs: a contractor quoting $28/lf installed for a 150 lf wood privacy fence is quoting $4,200 total, because fence labor and posts scale with the length of the run, not with the face area. Lumber sold by the board foot — the volume unit behind hardwood pricing — is a third system again; the board feet calculator linked above untangles it when you run into it at the hardwood counter.

Frequently Asked Questions

Conversion estimates only — confirm actual dressed widths with your supplier's spec sheet before ordering, and verify all framing sizes with your local building code.