menu_book What is a Linear Foot?
A linear foot (often abbreviated as LF or lin. ft.) is simply a one-foot length of any material. It is a one-dimensional measurement of straight line distance. Unlike square feet (which measures two-dimensional area) or board feet (which measures three-dimensional volume), a linear foot ignores width and thickness completely.
For example, if you purchase an 8-foot-long 2x4 board and an 8-foot-long 2x8 board, they both have exactly 8 linear feet, even though the 2x8 board is twice as wide and contains twice as much wood volume.
How to Calculate Linear Footage
To find the total linear feet needed for a project, use the following simple core formula:
If you are working with architectural measurements expressed in both feet and inches (e.g., 5 feet 6 inches), you must first convert the inches into a decimal fraction of a foot by dividing by 12:
- Formula: Inches ÷ 12 = Decimal Feet
- Example: 6 inches ÷ 12 = 0.5 feet. Therefore, 5 feet 6 inches = 5.5 feet.
- Example with fraction: 5' 6 1/2" -> 6.5 inches ÷ 12 = 0.5417 feet. Total length = 5.5417 feet.
Board Feet vs. Linear Feet: The Big Difference
While carpenters and DIYers calculate linear feet for purchasing trim, decking, or structural framing, wholesale lumber yards and hardwood dealers transact in board feet (BF). Board footage represents the volumetric measurement of rough-sawn lumber.
One board foot is defined as the volumetric equivalent of a wood piece that is 1 inch thick, 12 inches wide, and 1 foot long (equivalent to 144 cubic inches of material).
Crucial Lumber Industry Rule: When calculating board footage, you must use the nominal dimensions of lumber rather than actual dry-dressed dimensions. For instance, for a standard finished 2x4 (which physically measures 1.5" x 3.5"), you must use its nominal values (2" and 4") in the board feet equation.
Why Add a Wastage safety margin?
When buying timber, decking boards, metal joists, or trim moldings, never order the exact mathematical length required. Cross-cutting, board defects, splits, mistakes, and diagonal mitering inevitably reduce the net yield.
Standard building practice is to scale total linear footage with an overhead waste factor:
- 5% Waste Margin: Ideal for straight runs with uniform lengths (such as straight sub-floor joists).
- 10% Standard Margin: The standard safety buffer for general framing, roofing, and baseboard installation.
- 15% Waste Margin: Essential for complex deck grids with multi-angle herringbone patterns, herringbone tiles, or cabinetry molding where trim scrap volume is high.
Material Reference Conversion Table
| Material Type | Density (lb/ft³) | Standard Cut Waste | Primary Project Applications |
|---|---|---|---|
| Douglas Fir | 32.0 | 10% | Structural framing studs, rafters, and construction joists |
| Structural Steel | 490.0 | 5% | I-beams, architectural steel columns, structural reinforcing grids |
| Trex Composite | 60.0 | 12% | Composite deck surface boards, fascia, and high-durability steps |
| White Oak | 47.0 | 15% | High-end structural cabinetry, hardwood flooring, thresholds |
| Western Red Cedar | 23.0 | 10% | Outdoor pergolas, weather-resistant sidings, shingle trim |
