Board Feet vs Square Feet Calculator

This calculator converts between board feet and square feet for lumber. You enter the board thickness, width, and length (or the square footage and thickness), and it returns the equivalent volume in board feet or the area in square feet. The key difference is that board feet measure volume (1 ft × 1 ft × 1 in), while square feet measure area (1 ft × 1 ft).

Formula

The standard formula for board feet is:

Board Feet = (Length in feet × Width in inches × Thickness in inches) ÷ 12

Where:

• Length = lumber length in feet (ft)
• Width = lumber width in inches (in)
• Thickness = lumber thickness in inches (in)
• 12 = conversion factor (1 board foot = 144 cubic inches, and 1 ft × 12 in = 144 in²)

Square feet is simply length (ft) × width (ft). Since the width input is in inches, divide by 12 to get feet: Square Feet = (Length × Width) ÷ 12.

Worked Example

Using the default values: Length = 8 ft, Width = 6 in, Thickness = 1 in.

1. Board feet: (8 × 6 × 1) ÷ 12 = 48 ÷ 12 = 4.00 bd ft
2. Square feet: (8 × 6) ÷ 12 = 48 ÷ 12 = 4.00 ft²

For these dimensions, the board foot volume and square footage happen to be equal because the thickness is exactly 1 inch. Change the thickness to 2 inches and the board feet double (8.00) while the square footage stays 4.00.

Why the Confusion?

People often mix these units because both are used for lumber, but they measure different things. A square foot is a two-dimensional area—useful for flooring, siding, or drywall. A board foot is a three-dimensional volume—used for rough lumber, hardwood, and timber. A 1-inch-thick board that is 1 foot wide and 1 foot long is exactly 1 board foot and also 1 square foot of surface area. But if that board is 2 inches thick, it is still 1 square foot of face area yet 2 board feet of volume. The thickness is the entire difference.

When to Use Each

Choose the unit based on what you are buying or selling:

• Board feet: rough sawn lumber, hardwood, timber, any material sold by volume. Prices are quoted per thousand board feet (MBF).
• Square feet: finished flooring, plywood, sheet goods, siding, decking, anything sold by area coverage.
• Linear feet (not in this calculator) is yet another unit for length-only sales like trim or moulding.

If you are estimating how much lumber you need for a framing project, you will typically work in board feet for the studs and joists, but square feet for the sheathing. This calculator lets you switch between the two instantly.

Common Mistakes and Misconceptions

The most frequent error is forgetting to convert width and thickness to feet before multiplying. Board feet uses inches for width and thickness but feet for length, which is why the formula divides by 12, not by 144. Another mistake is assuming that a “2×4” actually measures 2 by 4 inches—it does not; a nominal 2×4 is 1.5 × 3.5 inches after planing. Always use the actual dimensions for board foot calculations unless you are buying rough lumber, where nominal and actual are the same.

Also note that board feet is a volume, so a 12-foot-long 2×4 (1.5 × 3.5 in) contains (12 × 3.5 × 1.5) ÷ 12 = 5.25 board feet, not 6.0 as you might guess from nominal sizes.

Cost Estimation

Once you have board feet, multiply by the price per board foot (often $2–$10 for hardwoods, less for softwoods). For square foot materials, multiply by the price per square foot. This calculator gives you the quantity; you supply the local price. Prices vary widely by species, grade, region, and current market conditions, so always check with your supplier.

Limitations of This Calculator

This calculator assumes rectangular, straight lumber. It does not account for waste, kerf (saw blade thickness), or defects like knots and warping. For a real project, add 10–20% extra for waste. It also does not convert between board feet and square feet directly unless you fix the thickness—the conversion depends entirely on thickness. For example, 100 board feet of 4/4 (1-inch) lumber equals 100 square feet, but 100 board feet of 8/4 (2-inch) lumber equals only 50 square feet.

Frequently Asked Questions

How do I convert board feet to square feet?

Divide the board feet by the thickness in inches. For example, 100 board feet of 1-inch-thick lumber = 100 ÷ 1 = 100 square feet. For 2-inch-thick lumber, 100 ÷ 2 = 50 square feet. This works because board feet already includes the thickness.

What is a board foot in metric?

A board foot is exactly 144 cubic inches, which equals 2,359.74 cubic centimeters (about 2.36 liters). In metric countries, lumber is usually sold by cubic meter (m³). One cubic meter equals 423.77 board feet.

Why do hardwood sellers use board feet instead of square feet?

Hardwood is sold by volume because thickness varies. A 4/4 (1-inch) and 8/4 (2-inch) board of the same length and width contain different amounts of wood. Board feet gives a fair price for the actual wood volume, regardless of how it is cut.

Does this calculator work for plywood?

Plywood and other sheet goods are sold by square footage (or by sheet, e.g., 4×8 = 32 ft²), not board feet. You can still use the square feet output, but ignore the board feet unless you are comparing volume. For a 3/4-inch sheet, the board feet would be 32 × 0.75 = 24 board feet, but that is not how plywood is priced.

What is the difference between nominal and actual lumber size?

Nominal size is the name (2×4, 1×6), while actual size is the real dimension after drying and planing. A 2×4 is actually 1.5 × 3.5 inches. For board feet calculations, use actual dimensions for finished lumber, but nominal for rough lumber. This calculator lets you enter either, just be consistent.

How many board feet are in a 2×4×8?

Using nominal dimensions: (8 × 4 × 2) ÷ 12 = 5.33 board feet. Using actual dimensions (1.5 × 3.5 × 8): (8 × 3.5 × 1.5) ÷ 12 = 3.5 board feet. Most lumberyards charge by nominal for softwood, so you pay for 5.33 bd ft. For hardwood, you pay by actual measured volume.

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in l | Length | ft | 8 | 0 | 1000
in w | Width | in | 6 | 0 | 120
in t | Thickness | in | 1 | 0 | 24
out bdft | Board Feet | bd ft | l * w * t / 12 | 2
out sqft | Square Feet | ft² | l * w / 12 | 2