How to Calculate Board Feet
Board feet is the standard unit for pricing and measuring rough-sawn and dimensional lumber volume — one board foot equals a piece of wood 12” × 12” × 1” (144 cubic inches).
Board feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
Worked example: A 2×6 board, 8 ft long, using actual dressed dimensions (1.5” × 5.5”): (1.5 × 5.5 × 8) ÷ 12 = 66 ÷ 12 = 5.5 board feet.
Note the distinction between nominal and actual size — a “2×6” is called that by its rough-cut size before drying and planing, but the actual finished board measures 1.5” × 5.5”. Some board-foot calculations use nominal dimensions (common in the lumber trade for pricing) while structural and material-quantity calculations should use actual dimensions — this calculator lets you choose which convention to apply.
| Nominal size | Actual (dressed) size |
|---|---|
| 1×4 | 3/4” × 3.5” |
| 1×6 | 3/4” × 5.5” |
| 1×8 | 3/4” × 7.25” |
| 2×4 | 1.5” × 3.5” |
| 2×6 | 1.5” × 5.5” |
| 2×8 | 1.5” × 7.25” |
| 2×10 | 1.5” × 9.25” |
| 2×12 | 1.5” × 11.25” |
| 4×4 | 3.5” × 3.5” |
| 4×6 | 3.5” × 5.5” |
| 6×6 | 5.5” × 5.5” |
Lumber Weight
Weight varies significantly by species and moisture content (kiln-dried vs. green/wet lumber). Rough planning densities:
| Wood type | Approx. weight per board foot |
|---|---|
| Kiln-dried SPF (spruce-pine-fir, standard framing) | ~2.5 lbs |
| Douglas fir (framing/structural) | ~2.9 lbs |
| Pressure-treated pine (wet from treatment process) | ~3.5–4.5 lbs |
| Cedar | ~2.1 lbs |
Worked example: 20 pieces of pressure-treated 2×6, 8 ft long (5.5 bf each = 110 total board feet) at ~4 lbs/bf ≈ 440 lbs total — a meaningful number to know before loading a trailer or truck bed.
Lumber Cost — Board Feet vs. Per-Piece Pricing
Lumber is priced two ways depending on the seller: per board foot ($/bf, common for hardwoods and specialty lumber) or per piece (common for standard dimensional construction lumber at big-box retailers). Larger commercial orders are often quoted per thousand board feet (MBF) — a “$/MBF” price divided by 1,000 gives the per-board-foot rate. This calculator lets you enter either format and converts automatically.
Lumber for Common Projects
- Deck framing: joists are typically 2×8, 2×10, or 2×12 depending on span — see our dedicated Deck Cost Calculator for a full material list including decking boards, not just structural framing lumber.
- Wall framing: standard interior/exterior walls use 2×4 or 2×6 studs, typically spaced 16” on center — total studs needed ≈ (wall length in ft × 12 ÷ 16) + 1, plus extra for corners and openings.
- Fencing: posts are commonly 4×4, set every 6–8 ft, with 1×6 or similar pickets between rails.
Frequently Asked Questions
How do I calculate board feet of lumber?
Multiply the board’s thickness in inches by its width in inches by its length in feet, then divide by 12. A 2×6 board (actual size 1.5”×5.5”) that’s 8 ft long is (1.5 × 5.5 × 8) ÷ 12 = 5.5 board feet.
What’s the difference between nominal and actual lumber size?
A “2×4” is its nominal (rough-cut) size — the actual, dressed size after drying and planing is smaller, at 1.5” × 3.5”. Board-foot and material calculations should generally use actual dimensions, while lumber-yard pricing sometimes uses nominal sizing by convention.
How much does a piece of lumber weigh?
Weight depends heavily on species and moisture content — kiln-dried SPF framing lumber runs roughly 2.5 lbs per board foot, while wet pressure-treated pine can weigh 3.5–4.5 lbs per board foot due to the treatment chemicals and retained moisture.
How much lumber do I need for a deck?
Deck framing typically uses 2×8, 2×10, or 2×12 joists depending on your span and load requirements, spaced 16” on center, plus a rim/ledger board and posts. Use our Deck Cost Calculator for a complete material list including decking boards.
How much lumber do I need for framing a wall?
For standard 16” on-center framing, divide the wall’s length in inches by 16 and add 1 for the extra stud, then add studs for each corner and opening (doors/windows typically need extra king and cripple studs around them).
How is lumber priced — per board foot or per piece?
Both, depending on the seller. Hardwoods and specialty lumber are commonly priced per board foot ($/bf); standard construction dimensional lumber at retailers is usually priced per piece. Large commercial orders are often quoted per thousand board feet (MBF).
How much lumber do I need for a fence?
Posts are typically 4×4, spaced every 6–8 feet along the fence line, with horizontal rails (usually 2×4) and vertical pickets (commonly 1×6) filling the spans between posts.
What size lumber should I use for framing?
2×4 is the traditional standard for interior and many exterior walls; 2×6 is increasingly common for exterior walls to allow more insulation depth. Structural spans (joists, headers, beams) need sizing based on load and span — consult span tables or a structural engineer for anything load-bearing beyond standard residential framing.
Can I use this instead of a lumber yard’s own calculator?
Yes, as an independent, brand-agnostic estimate to sanity-check any supplier’s quote. Always confirm exact grade, species, and current pricing with your specific lumber yard before ordering.
How do I convert board feet to linear feet?
Board feet accounts for thickness and width as well as length, so the conversion depends on the board’s dimensions — divide total board feet by (thickness × width ÷ 12) to get linear feet for a given board size. The calculator above shows both figures automatically.
Get free quotes from local carpentry & framing contractors
Confirm grade, species, and current yard pricing before you order. A contractor quote helps if you need framing labor too.