How to Calculate Linear Feet (and Convert Square Feet to Linear Feet)
Linear feet measure length only. To convert square feet to linear feet, multiply by 12 and divide by the board width in inches: 100 sq ft of 5.5 in wide boards is 100 × 12 ÷ 5.5 = 218.18 linear feet.
What is a linear foot?
A linear foot is 12 inches of length, measured in a straight line along one dimension. It says nothing about width or thickness. A 1×6 board that is 8 ft long is 8 linear feet, and so is an 8 ft board that is 12 inches wide. Linear feet are how trim, baseboard, lumber, fencing runs, gutters and edging are priced and counted.
Square feet describe a surface: length times width. To switch between the two you need the width of the material, because the same area takes more length of a narrow board than of a wide one. Freight carriers also use the words "linear feet" for the length of trailer floor a shipment occupies. That is a shipping measure and does not follow the width formula below.
The formula
linear feet = square feet × 12 ÷ board width (in)
square feet = linear feet × board width (in) ÷ 12Here is why it works. A board 1 ft (12 in) long and w inches wide covers 12 × w square inches. One square foot is 144 square inches, so each linear foot covers 12 × w ÷ 144 = w ÷ 12 square feet. Flip that to get linear feet per square foot: 12 ÷ w. Use the actual width of the board, not the nominal name, and add the gap between boards if there is one. If you first need the area, see how to calculate square feet.
How many linear feet are in 100 square feet?
It depends on the board width. These widths are the actual (dressed) widths of common boards: a 1×6, 2×6 and 5/4×6 decking board are all 5-1/2 in wide, and a 1×4 is 3-1/2 in wide.
| Actual board width | Nominal size | Linear ft per 100 sq ft | Sq ft covered by 100 linear ft | Linear ft per 1 sq ft |
|---|---|---|---|---|
| 2-1/2 in | 1×3 | 480.00 | 20.83 | 4.80 |
| 3-1/2 in | 1×4 | 342.86 | 29.17 | 3.43 |
| 5-1/2 in | 1×6, 2×6, 5/4×6 | 218.18 | 45.83 | 2.18 |
| 7-1/4 in | 1×8 | 165.52 | 60.42 | 1.66 |
| 9-1/4 in | 1×10 | 129.73 | 77.08 | 1.30 |
| 11-1/4 in | 1×12 | 106.67 | 93.75 | 1.07 |
| 12 in | 12 in wide | 100.00 | 100.00 | 1.00 |
The table shows exact coverage with no gaps, cuts or waste. Trim, flooring and other products are made in many widths, so use the width printed on the product. For any width, divide 1,200 by the width in inches to get linear feet per 100 sq ft.
The linear feet calculator converts square feet to linear feet and back for any width, counts pieces of stock and works out baseboard for a room. If you first need the area, add up rooms and surfaces in feet and inches with the square footage calculator. For decks, the deck calculator counts rows, boards and linear feet with the gap built in.
Open the linear feet calculator Open the square footage calculator Open the deck calculator
How do you calculate linear feet of baseboard?
Trim runs along the edge of a room, so you need the perimeter, not the area. Add up the length of each wall you will cover, then subtract openings such as doorways.
Example: a 12 ft × 15 ft room with two 3 ft doorways.
- Perimeter: 2 × (12 + 15) = 54 ft
- Minus two doorways: 54 − (2 × 3) = 48 linear feet
- With a 10% allowance for mitered corners and scrap (an example figure, adjust to your job): 48 × 1.10 = 52.8 linear feet
- In 8 ft pieces: 52.8 ÷ 8 = 6.6, so buy 7 pieces
If you add up several rooms, round up once at the end, not room by room. Closets and alcoves add their own wall lengths. Because baseboard height does not change the linear footage, you only need the width formula if you are converting an area of trim. For a whole floor, 8, 12 and 16 ft pieces and a table, see how much baseboard you need.
How many linear feet of flooring planks do you need?
Plank flooring is sold by the box in square feet, which is the number to buy by. Linear feet are useful when you want to know how many plank lengths a room takes or how long the rows run. Start with the room area plus waste. Retailer guidance puts straight-lay waste at about 7% to 10%, and the box label wins if it differs.
Example: a 12 ft × 15 ft room, planks 5 in wide, 10% waste.
- Area: 12 × 15 = 180 sq ft
- With waste: 180 × 1.10 = 198 sq ft
- Linear feet of plank: 198 × 12 ÷ 5 = 475.2 linear feet
- If planks are 4 ft long: 475.2 ÷ 4 = 118.8, about 119 planks
Planks come in boxes, so order by the coverage printed on the carton and round up to a whole box.
How many linear feet of decking do you need?
Decking is where the gap matters. Boards sit apart so water can drain and the wood or composite can expand, so each row uses the board width plus the gap. Gap size is product specific, so follow the manufacturer’s gapping guidance.
Example: a 12 ft × 16 ft deck, 5.5 in boards, 1/4 in gaps.
- Area: 12 × 16 = 192 sq ft
- Ignoring gaps: 192 × 12 ÷ 5.5 = 418.91 linear feet
- With gaps, each row takes 5.5 + 0.25 = 5.75 in: 192 × 12 ÷ 5.75 = 400.70 linear feet
- By rows: 144 in ÷ 5.75 in = 25.04 rows, so you need 26 rows. 26 rows × 16 ft = 416 linear feet
The area formula gives 400.70 and the row count gives 416. You cannot buy 0.04 of a row, so the row method is the one to order from; it is what the deck calculator uses. For boards by length, waste and joist layout, see how many deck boards you need. Deck framing, footings, ledgers and railings are structural and regulated by local code, and this guide counts boards only.
How do you convert linear feet to square feet?
Multiply the length by the width in feet. With the width in inches, use linear feet × width ÷ 12. For 250 linear feet of 3.5 in wide trim board: 250 × 3.5 ÷ 12 = 72.92 sq ft. If the width is already 12 inches, linear feet and square feet are the same number.
Linear feet, square feet and board feet
| Unit | What it measures | Formula | Typical use |
|---|---|---|---|
| Linear foot | Length | Length in feet | Trim, boards, fence runs, edging |
| Square foot | Area | Length × width (ft) | Flooring, decking, drywall, roofing |
| Board foot | Volume of lumber | Thickness (in) × width (in) × length (ft) ÷ 12 | Lumber and hardwood pricing |
Board feet add thickness to the picture. See how to calculate board feet for that formula, and cubic feet and cubic yards for volume in bulk materials. Framing a wall counts pieces instead: see how many studs you need.
Common mistakes
- Converting without a width. Square feet cannot become linear feet until you know how wide the material is.
- Using the nominal size. A 1×6 is 5-1/2 in wide, not 6 in. Measure the board or read the label.
- Forgetting the gap. Decking and some siding have spacing that adds to each row.
- Skipping waste. Cuts, end trimming and defects mean you buy more than the exact figure.
- Mixing lengths. Count linear feet first, then divide by the stock length and round up to whole pieces.
- Not subtracting openings for trim. Doorways have no baseboard.
Questions people ask
How do you convert square feet to linear feet?
Multiply square feet by 12, then divide by the material width in inches. For 100 sq ft of 3.5 in wide boards: 100 × 12 ÷ 3.5 = 342.86 linear feet.
How many linear feet are in a square foot?
It depends on the width. A 12 in wide board gives 1 linear foot per square foot, a 5.5 in board gives 2.18 and a 3.5 in board gives 3.43.
How many linear feet are in 100 square feet?
Divide 1,200 by the board width in inches. That is 218.18 linear feet for 5.5 in boards and 165.52 for 7.25 in boards, before waste and gaps.
How do you measure linear feet of a room?
Add the length of every wall you will cover, which is the perimeter for a rectangular room: 2 × (length + width). Subtract door openings for baseboard. A 12 ft × 15 ft room has 54 ft of perimeter.
Is a linear foot the same as a lineal foot?
Yes, both mean one foot of length. "Linear foot" is the usual spelling in US building supply and is the term used in this guide.
Sources
- Architect’s Toolbox, Lumber Dimensions (secondary source). Actual widths of 1x and 2x boards and 5/4×6 decking, citing the PS 20 lumber standard. Accessed October 16, 2026.
- Lumber Liquidators, Estimating your DIY flooring project (retailer guidance). Straight-lay waste of 7% to 10%. Accessed October 16, 2026.
- Trex, Six tips for planning a successful deck build. Follow the manufacturer’s gapping guidelines. Accessed October 16, 2026.
- NIST, Handbook 44 (2026), Appendix C: General Tables of Units of Measurement. Foot, inch and square foot definitions. Accessed October 16, 2026.