How to Calculate Board Feet

Board feet are calculated by multiplying a board's three dimensions — thickness, width, and length — and dividing by 12. There are two equivalent formulas depending on the units you use for length. This guide walks through both formulas, four worked examples, NHLA hardwood rules, and the most common calculation mistakes.

The Two Board Foot Formulas

Both formulas give identical results. Formula 1 (÷12) is more common in US woodworking because lumber length is usually expressed in feet. Formula 2 (÷144) is useful when all three dimensions come from the same measurement system (e.g., a tape measure reading everything in inches).

Step-by-Step Examples

Example 1: Standard 2×4×8 Framing Stud

1. Thickness = 2 inches (nominal)
2. Width = 4 inches (nominal)
3. Length = 8 feet
4. BF = (2 × 4 × 8) ÷ 12 = 64 ÷ 12 = 5.33 board feet

If you use actual dimensions (1.5" × 3.5"): (1.5 × 3.5 × 8) ÷ 12 = 42 ÷ 12 = 3.50 board feet. The difference — 5.33 vs 3.50 — is significant when pricing large quantities.

Example 2: 4/4 Hardwood Board (1" × 8" × 6')

1. Thickness = 1 inch (4/4 nominal)
2. Width = 8 inches
3. Length = 6 feet
4. BF = (1 × 8 × 6) ÷ 12 = 48 ÷ 12 = 4.00 board feet

Example 3: 8/4 Walnut Slab (2" × 14" × 7')

1. Thickness = 2 inches (8/4)
2. Width = 14 inches
3. Length = 7 feet
4. BF = (2 × 14 × 7) ÷ 12 = 196 ÷ 12 = 16.33 board feet

At $12/BF, this slab costs roughly $196. At $18/BF for figured walnut, the same slab is $294.

Example 4: Multiple Boards

For multiple identical boards, multiply by quantity:

10 boards of 2×6×12': (2 × 6 × 12) ÷ 12 × 10 = 12 × 10 = 120 board feet

For mixed sizes, calculate each separately and sum the results. Use the Lumber Estimator to handle multiple sizes at once with pricing and waste allowance built in.

Estimating Cost from Board Feet

Once you have a board foot total, multiply by the price per board foot:

Softwood framing lumber typically runs $3–$6/BF at retail. Domestic hardwoods range from $5–$15/BF. Figured or exotic species can exceed $20/BF. The Lumber Estimator lets you enter your price per BF or per MBF and calculates project cost automatically.

Quick Reference: Board Feet per Length

→ Full interactive board foot chart for more sizes and lengths

NHLA Tally Mode (Hardwood)

Hardwood lumber is tallied by NHLA (National Hardwood Lumber Association) rules, which differ slightly from simple geometric calculation:

• Thickness rounds up to the next ¼-inch (e.g., a board measured at 15/16" is tallied as 4/4 = 1")
• Any board thinner than 4/4 is tallied as 4/4 — the minimum
• Length rounds down to the nearest whole foot (a board that is 8'11" is tallied as 8')

These asymmetric rounding rules exist to protect buyers: you always get at least the thickness you paid for, but you don't get credit for a few inches of extra length. The Board Foot Calculator has a "Hardwood tally (NHLA)" toggle that applies these rules automatically.

Common Mistakes When Calculating Board Feet

• Mixing units within the formula. The most frequent error: entering length in inches when the formula expects feet, or mixing inches and feet for thickness and width. Always check which unit each variable expects before plugging in numbers.
• Using actual dimensions when nominal is appropriate (or vice versa). Lumber yards price by nominal board feet. If you calculate with actual dimensions, your estimated cost will be too low — you'll order less than you need. Use nominal for ordering, actual for true volume.
• Forgetting NHLA rounding direction for hardwood. Thickness rounds up; length rounds down. Getting this backwards (rounding length up) overstates board footage and inflates cost estimates.
• Not accounting for waste. Cutting, defects, and planing loss typically consume 10–20% of purchased lumber. Add a waste factor before ordering. The Lumber Estimator has a built-in waste percentage field.
• Calculating board feet for rough-sawn logs. Board foot formulas apply to rectangular lumber. Logs require a log rule (Doyle, Scribner, or International ¼") to estimate yield. See the Log Scale Calculator.

Nominal vs Actual — Which to Use?

Use nominal dimensions when you're ordering lumber at a store or mill — they price by nominal board feet. Use actual dimensions when you need the true volume of wood (for engineering, weight calculations, or export quotes in cubic meters). Most woodworkers and contractors use nominal.

→ Nominal vs actual lumber dimensions — full reference with size table

Use the Calculator

For quick calculations with any combination of dimensions, fractions, multiple boards, pricing, and waste allowance:

→ Board Foot Calculator

Frequently Asked Questions