How to Calculate Board Feet
Formula: Board Feet (BF) = (thickness × width × length) ÷ 12. All dimensions in inches and feet as marked. Total BF = BF per piece × quantity.
Related: Try our deck calculator, fence calculator, or stair calculator for your project.
Nominal vs Actual Sizes
| Nominal | Actual (inches) |
|---|
| 1×2 | 3/4 × 1-1/2 |
| 1×4 | 3/4 × 3-1/2 |
| 2×4 | 1-1/2 × 3-1/2 |
| 2×6 | 1-1/2 × 5-1/2 |
| 2×8 | 1-1/2 × 7-1/4 |
| 2×10 | 1-1/2 × 9-1/4 |
| 2×12 | 1-1/2 × 11-1/4 |
| 4×4 | 3-1/2 × 3-1/2 |
Note: Board feet are calculated using nominal dimensions, not actual dimensions. This is the standard industry practice for pricing.
Lumber Types and Best Uses
Choosing the right lumber for your project affects cost, durability, and appearance. The two broad categories are softwoods (fast-growing, affordable, structural) and hardwoods (dense, durable, finish work).
| Species | Common Uses | $/BF (approx) | Notes |
|---|
| SPF (spruce-pine-fir) | Framing, studs, joists | $0.50–$1.00 | Most common construction lumber |
| Pressure-treated pine | Decks, fences, ground contact | $0.80–$1.50 | Chemical-treated for rot/insect resistance |
| Cedar | Decking, siding, closets | $1.50–$3.00 | Natural rot resistance, aromatic |
| Redwood | Premium decking, outdoor furniture | $2.00–$5.00 | Beautiful grain, very durable |
| Oak (red/white) | Furniture, flooring, trim | $4.00–$8.00 | Hardwood, strong, stainable |
| Poplar | Paint-grade trim, drawers | $2.50–$4.00 | Soft hardwood, paints well |
| Plywood (ACX) | Sheathing, subfloors | $1.00–$2.00/sq ft | Sold by sheet, not board foot |
How Much Lumber for Common Projects
| Project | Key Lumber | Typical Quantity |
|---|
| 12×16 deck | 2×8 joists, 5/4×6 decking, 6×6 posts | ~28 deck boards, ~13 joists, ~6 posts |
| 100 ft wood fence | 4×4 posts, 2×4 rails, 1×6 pickets | ~14 posts, ~42 rails, ~300 pickets |
| 8×10 shed | 2×4 framing, 4×4 skids, T1-11 siding | ~30 2×4×8, 4 4×4×10, 6 sheets siding |
| Standard staircase | 2×12 stringers, 2×10 treads, 4×4 posts | 3 stringers, ~6 treads, 2 posts |
| 10×12 pergola | 6×6 posts, 2×8 beams, 2×6 rafters | 4 posts, 2 beams, ~10 rafters |
Use our deck calculator and fence calculator for precise material lists on those projects.
How to Choose and Buy Lumber
- Check the grade stamp. #2 grade is fine for framing. #1 or "select" has fewer knots for visible work. "Stud" grade is for wall studs only.
- Inspect each board. Look down the edge for straightness — reject crowned, bowed, or twisted boards. Small tight knots are fine; large loose knots weaken the board.
- Check moisture content. Framing lumber should be 19% or less (KD-HT stamped). Green lumber will shrink and warp as it dries.
- Buy 10–15% extra. For cuts, defects, and mistakes. Return unused full-length boards within the store's return window.
- Compare unit pricing. Big-box stores price per piece; lumberyards price per board foot. Calculate the per-foot cost to compare.
Storage and Handling
- Store flat on level supports (4×4s or blocks) spaced every 3–4 ft to prevent sagging.
- Keep dry. Cover with a tarp but leave sides open for airflow. Never store lumber directly on the ground.
- Acclimate before use. Bring interior trim indoors 3–7 days before installation so it adjusts to room humidity.
- Seal cut ends. On pressure-treated lumber, coat field cuts with copper naphthenate preservative to maintain the warranty.
Common Mistakes
- Using actual size for calculations. Always use nominal dimensions for board foot math. A 2×4 is 1.5×3.5 actual but priced as 2×4.
- Ignoring load ratings. Not all 2×10s are equal — check the grade stamp's Fb (bending) and E (modulus of elasticity) values for structural applications.
- Mixing treated and untreated. Use corrosion-resistant (stainless or hot-dip galvanized) fasteners with ACQ-treated lumber; regular screws will corrode.
- Buying too little. A second trip to the store risks a different mill run with slight color or size variation. Buy extra and return leftovers.
- Not accounting for kerf. A saw blade removes ~1/8" per cut. When cutting multiple pieces from one board, add the kerf to your total length.
FAQ
What is a board foot?
1 BF = 1" thick × 12" wide × 12" long = 144 cu in. Formula: (T × W × L) ÷ 12.
Why is 2×4 not 2×4?
Nominal size is rough-cut green dimension. After drying and planing, 2×4 = 1.5×3.5 inches actual.
Board feet in 2×4×8?
(2 × 4 × 8) ÷ 12 = 5.33 BF per piece. 10 pieces = 53.3 BF.
Lumber cost per BF?
Pine $0.50-1.50/BF, cedar $1.50-3/BF, hardwoods $3-8/BF. Prices fluctuate with market.