Square Feet to Linear Feet Calculator

Use the Width You Measured, Not the Name on the Pile

The single most common ordering mistake on this conversion is dividing by the name of the stock instead of the face width you can measure with a tape. Lumber and flooring are sold by nominal size and milled smaller:

Dividing by 6 when the board is 5.5 in wide asks 100 sq ft to be covered by 200 linear feet of board that can only cover 91.7 sq ft of it — about 9% short, before a single cross-cut. Measure three boards from the bundle you actually bought and use that number.

Where the "nominal means something smaller" rule comes from

This is not a yard convention you can argue with at the counter; it is written into the standard. The US Department of Agriculture Forest Service's lumber chapter states it flatly:

“Lumber length is recorded in actual dimensions, whereas width and thickness are traditionally recorded in "nominal" dimensions--actual dimensions are somewhat less.”

The same chapter points at the authority for the exact numbers:

“To standardize and clarify nominal to actual sizes, the American Softwood Lumber Standard PS-20 specifies the actual thickness and width for lumber that falls under the standard.”

American Softwood Lumber Standard PS 20-20 defines the term itself:

“Nominal size-- The label designation for lumber size categories that does not reflect the dressed size.”

The same standard also warns against reading the label as a measurement:

“No inferences shall be drawn that the "nominal" sizes are dressed sizes.”

PS 20-20's own example is the 2 × 4 everyone knows — “a dry 2 by 4 is surfaced to 38.1 mm by 88.9 mm (1 1/2 by 3 1/2 inches)” — the same 1/2 in of removal per dimension that turns a nominal 6 in board into a 5.5 in face.

So when a decking bag says "6 in", the number that belongs in the width field is the one your tape gives you. PS 20-20 is a voluntary product standard published by NIST, and the USDA Forest Service chapter is a general technical report; both are linked in the sources below if you want to read the dressed-size tables yourself.

Leave the width field at the face width. If you deliberately want gaps — a deck you want to drain, a fence you want to see through — the gap does not consume board length; it opens up area the wood never covers. Then the area you need to buy wood for is the covered share, so the face width stays in the divisor.

Fences Have Three Different Divisors

Picket fences are where this conversion goes wrong most often, because "6 in picket" and "6 ft of fence" are not the same measurement:

• Solid stockade, pickets butted edge to edge: coverage per picket is its full face width, so use that width — 5.5 in pickets behind 100 sq ft of fence face need 218 linear feet.
• Spaced pickets (dog-trot or shadow-box look): each picket is centered one picket-width plus one gap apart, so the wood you need falls while the fence still spans the same area. For 5.5 in pickets at 1 in gaps the wood covers 5.5 ÷ 6.5 = 84.6% of the face, so 100 sq ft of fence line takes about 185 linear feet of picket, not 218.
• Board-on-board with overlap: each picket covers its width minus the overlap on both rails' sides. A 6 in picket with 1 in of overlap each side covers 4 in of face, so use 4 in as the width: 100 sq ft of face needs 300 linear feet.

Rails and posts are not this calculation at all — they are priced by the stick. Measure the run length for rails and add the number of post holes; do not run them through an area-to-length conversion.

From Linear Feet to a Buying List

Linear feet is a yardstick, not an order. Two more steps turn it into what you carry out of the yard:

1. Add the cuts. Cross-cuts at walls and corners, the offcut at the start of each row that is too short to reuse, and boards you cull for knots or warp are where the waste comes from. 10% is the usual starting allowance for a straight lay in a square room; 15% for diagonal or herringbone layouts, or for a long run with many obstructions. Nothing fixes that number for your job — measure the room's perimeter and let the layout decide.
2. Divide by the length you can actually buy. 264 linear feet in 8-foot boards is 33 boards. Mixed lengths in one order do not change the total length, but they do change how many partial boards you finish a row with, so buy the longest length your room's longest run allows.

Worked: 100 sq ft of 5.5 in decking is 218.2 net linear feet. At 10% that is 240 linear feet, which is 30 boards at 8 ft each.

Board feet, if the yard quotes that way. A board foot is a volume — 12 in × 12 in × 1 in, which is 144 cubic inches. Convert with linear feet × width in ÷ 12 × thickness in. 218.2 linear feet of 5.5 in stock at 1 in thick is 100 board feet; the same boards 2 in thick is 200 board feet.

Worked Example: 340 Sq Ft of Deck, One Trip to the Yard

You are re-planking a 340 sq ft deck with nominal 1 × 6 decking, buying 8-foot boards, and you want a 10% cutting allowance. Run those four numbers through the widget above and check it against the arithmetic line by line:

1. Face width, not the name. A nominal 6 in deck board dresses to 5.5 in, so 5.5 goes in the width field (USDA Forest Service: “width and thickness are traditionally recorded in "nominal" dimensions--actual dimensions are somewhat less.”).
2. Net linear feet. 340 × 12 ÷ 5.5 = 741.8 linear feet of board face to cover the deck with no gaps and no cuts.
3. Waste allowance. 741.8 × 1.10 = 816.0 linear feet to order. At 10% for a straight lay this is the usual starting figure; a herringbone deck or a lot of mitered borders would take more.
4. Boards. 816 ÷ 8 = 102 boards. That divides exactly this time, but it usually does not — 100 sq ft of 5 in plank needs 264 linear feet, which is 33 boards.
5. What you are actually carrying. 102 boards × 8 ft = 816 linear feet, or 74.2 linear feet more than the deck needs (816 − 741.8). That surplus is the cutting allowance; it is real offcuts, not a rounding artifact.

The last two rows are the same lumber counted two ways, and the gap is not a mistake. PS 20-20 defines the trade tally on the label size:

“The number of board feet in a piece of lumber is obtained by multiplying the nominal thickness in inches or fraction of an inch by the nominal width in feet by the length in feet.”

408 ÷ 374 − 1 = 9.1% more board feet than the dressed boards contain — which is the nominal/actual width gap (6 ÷ 5.5) showing up in the volume column. If you are comparing a per-board-foot price against a per-linear-foot price, that 9.1% is the whole difference; ask which dimension the quote used before you call one cheaper.

Everything in this example is one multiplication and one division: 340 × 12 ÷ 5.5, × 1.1, ÷ 8, and 816 × 5.5 ÷ 12 versus 816 × 0.5. The widget above reproduces each step as you type.

Quick Reference (100 sq ft)

Board counts round up to whole boards, which is why they carry slightly more than the 10% waste already added.