Board Foot Calculator
Calculate board feet for single boards or multiple lumber pieces — with preset sizes, cost estimation, and waste allowance.
Working with plywood sheets? Calculate quantities and costs with our Plywood Calculator.
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How It Works
Board Feet = Thickness (in) × Width (in) × Length (ft) ÷ 12. One board foot equals 144 cubic inches (12″×12″×1″). Nominal lumber sizes differ from actual — a 2×4 is actually 1.5″×3.5″.
Understanding Board Foot Calculation
A board foot is the standard unit of measurement for lumber in North America. Understanding how to calculate board feet is essential for estimating material costs and quantities in woodworking and construction.
Calculation Formulas
One board foot equals a piece of lumber 12 inches wide, 12 inches long, and 1 inch thick (144 cubic inches).
Nominal vs. Actual Lumber Sizes
Lumber is sold by nominal dimensions, but the actual sizes are smaller due to planing and drying:
| Nominal | Actual (in) | Board Feet per 8′ length |
|---|---|---|
| 2×4 | 1.5 × 3.5 | 3.50 |
| 2×6 | 1.5 × 5.5 | 5.50 |
| 2×8 | 1.5 × 7.25 | 7.25 |
| 2×10 | 1.5 × 9.25 | 9.25 |
| 4×4 | 3.5 × 3.5 | 9.33 |
| 6×6 | 5.5 × 5.5 | 22.00 |
How to Calculate Board Feet
Woodworking & Construction Applications
- Material estimation: Calculate lumber volume for framing, decking, and woodworking projects.
- Cost calculation: Estimate total lumber cost by multiplying board feet with price per BF.
- Inventory planning: Convert between board feet and linear feet for ordering.
- Framing: Estimate wall plates, studs, and rafters in board feet.
- Hardwood purchasing: Hardwood is typically sold by the board foot at lumber yards.
Frequently Asked Questions
What is a board foot?
A board foot is a volume measurement equal to 144 cubic inches — a piece of lumber 12 inches wide, 12 inches long, and 1 inch thick. The formula is: Board Feet = Thickness (in) × Width (in) × Length (ft) ÷ 12.
Why are nominal and actual lumber sizes different?
Lumber is milled to its nominal size when green (wet), then planed smooth and dried. This process reduces the dimensions. A nominal 2×4 actually measures 1.5″×3.5″. Always use actual dimensions when calculating board feet for accuracy.
How many board feet are in a 2×4×8?
Using actual dimensions (1.5″×3.5″×8′): Board Feet = 1.5 × 3.5 × 8 ÷ 12 = 3.5 BF. Using nominal dimensions (2″×4″×8′): 2 × 4 × 8 ÷ 12 = 5.33 BF. The actual board foot count of 3.5 BF is what you should use for cost estimation.
How much waste should I add for lumber?
A 10% waste allowance is standard for most projects. Use 5% for simple projects with few cuts, 15% for projects with many angles or curves, and up to 20% for rough-sawn lumber that may have defects or warping.
What is the difference between board feet and linear feet?
Linear feet measures only length, while board feet measures volume (thickness × width × length). A 2×4 and a 2×8 both have 8 linear feet in an 8-foot piece, but the 2×4 contains 3.5 BF while the 2×8 contains 7.25 BF. Board feet accounts for the cross-section size.