Linear feet to square feet

How do I convert linear feet to square feet?

Multiply the linear feet by the board width in feet — the width in inches divided by 12. 100 linear feet of 5½ inch boards covers 100 × 5.5 ÷ 12 = 45.8 square feet.

How do I convert square feet to linear feet?

Divide the square feet by the board width in feet: square feet × 12 ÷ width in inches. To cover 200 square feet with 5½ inch boards you need 200 × 12 ÷ 5.5 = 436.4 linear feet.

Should I use the nominal or the actual width?

The actual width. A 1×6, a 2×6 and a 5/4×6 deck board are all 5½ inches wide, not 6. For tongue-and-groove or shiplap, use the face width that shows once the boards are fitted together.

How do I count linear feet for deck boards with gaps?

Add the gap to the board width. With 5½ inch boards and ¼ inch gaps each board covers 5¾ inches, so 200 square feet takes 200 × 12 ÷ 5.75 = 417.4 linear feet.

How many boards is that?

Divide the linear feet by the length of one board and round up. 436.4 linear feet of 12 ft boards is 36.4, so 37 boards — plus some extra for cuts and bad boards.

What is the difference between linear feet and board feet?

Linear feet measure length only. A board foot is a unit of volume: the wood in a piece 1 inch thick, 12 inches wide and 12 inches long. Boards sold by the linear foot (trim, decking, shiplap) never need the thickness; hardwood sold by the board foot does.

Does the result include waste?

No. The calculator returns the exact length that covers the area. Cuts at the ends, bad boards and angled layouts need extra material on top, and the amount depends on the job.

How the conversion works

Each board covers its face width times its length, so square feet = linear feet × (width + gap) ÷ 12, with the width and gap in inches. Solving for length gives linear feet = square feet × 12 ÷ (width + gap). The gap is counted because the space between boards is part of the surface you are covering. The calculation treats the surface as a rectangle filled edge to edge; it does not know about angled cuts, borders or boards that stop at a wall. The last board in a row has no gap after it, so the result runs very slightly high, which errs on the safe side.

Worked example: a 12 by 16 ft deck

The deck is 192 square feet. Decking boards are 5½ inches wide and will be laid with a ¼ inch gap, so each board covers 5.75 inches of the surface. Linear feet = 192 × 12 ÷ 5.75 = 400.7 linear feet. With 16 ft boards that is 25.04, so 26 boards: the fraction always rounds up, because a board cannot be bought in parts. Checking in reverse, 400.7 linear feet × 5.75 ÷ 12 gives back 192 square feet.

Mistakes to avoid

Using the nominal width is the usual one. Entering 6 inches instead of the actual 5½ with the same gap gives 368.6 linear feet, which is 32.1 feet short, enough to leave rows unfinished. Second, do not mix units: a board price per linear foot and a coverage in square feet are different numbers, so convert first and then multiply by the price. Third, count the gap only when the boards really are spaced; tongue-and-groove and shiplap have none, and their face width is what shows after fitting.

Sources: actual dressed widths of 1×6, 2×6 and 5/4×6 boards (5½ in) are from the American Softwood Lumber Standard, PS 20. The conversions are plain geometry. Related tools: deck calculator, board foot calculator, lumber calculator, square footage calculator.