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Lumber Calculator

Calculate board feet, estimate lumber costs, and convert between nominal and actual dimensions.

Board Feet Calculator

Add lumber pieces to calculate total board feet and cost. Board feet = (thickness × width × length) ÷ 12, where thickness and width are in inches and length is in feet.

Thickness: Width: in Length: ft Qty:
$

Nominal vs Actual Lumber Dimensions

Lumber is sold by nominal size but the actual dimensions are smaller after drying and planing.

Nominal (in)Actual (in)Actual (mm)
1 × 20.75 × 1.519 × 38
1 × 30.75 × 2.519 × 64
1 × 40.75 × 3.519 × 89
1 × 60.75 × 5.519 × 140
1 × 80.75 × 7.2519 × 184
1 × 100.75 × 9.2519 × 235
1 × 120.75 × 11.2519 × 286
2 × 21.5 × 1.538 × 38
2 × 41.5 × 3.538 × 89
2 × 61.5 × 5.538 × 140
2 × 81.5 × 7.2538 × 184
2 × 101.5 × 9.2538 × 235
2 × 121.5 × 11.2538 × 286
4 × 43.5 × 3.589 × 89
4 × 63.5 × 5.589 × 140
6 × 65.5 × 5.5140 × 140

Quick Dimension Converter

Enter a nominal lumber size to see its actual dimensions.

0.75" × 3.5" (19 mm × 89 mm)

How It Works

Board Feet

A board foot is a unit of volume for lumber equal to 144 cubic inches. It represents a piece of wood 1 inch thick, 12 inches wide, and 1 foot long.

  1. Board feet per piece = (thickness in inches × width in inches × length in feet) ÷ 12
  2. Subtotal board feet = board feet per piece × quantity
  3. Waste allowance = subtotal × waste percentage
  4. Total board feet = subtotal + waste allowance
  5. Estimated cost = total board feet × price per board foot
Nominal vs Actual Sizes

When you buy a "2×4" from the lumber yard, its actual dimensions are 1.5" × 3.5". This is because:

  • Green lumber is cut to nominal size when freshly sawn
  • Drying causes the wood to shrink
  • Planing smooths the surfaces, removing more material
  • The nominal name is kept for convenience and industry convention
Common Lumber Prices

Prices vary widely by species, grade, and region. Typical ranges per board foot:

  • Pine / SPF (construction): $2 – $5 per BF
  • Poplar: $3 – $6 per BF
  • Red Oak: $4 – $8 per BF
  • Hard Maple: $5 – $10 per BF
  • Cherry: $6 – $12 per BF
  • Walnut: $8 – $15 per BF
Tips
  • Always add 10–15% waste allowance for cuts, defects, and mistakes
  • Board feet calculations use nominal dimensions — this is lumber industry standard
  • For projects using dimensional lumber (2×4s, etc.), consider buying by the linear foot instead
  • Check boards for straightness, knots, and moisture content before purchasing

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