Lumber Calculator

Data Source & Methodology

Calculations for lumber volume, board feet, and weight are based on standard industry formulas and data published by the USDA Forest Products Laboratory in the "Wood Handbook: Wood as an Engineering Material" (General Technical Report FPL-GTR-282).

• Volume & Board Feet: Based on Chapter 2, "Characteristics and Availability of Commercially Important Woods."
• Weight & Density: Based on Chapter 4, "Physical Properties and Moisture Relations," using specific gravity and moisture content.

All calculations are based strictly on the formulas and data provided by this source. Framing estimates use standard "on-center" spacing rules with an allowance for end-studs and plates.

The Formulas Explained

1. Board Foot (BF)

A board foot is a unit of volume for lumber, equivalent to one square foot of wood that is one inch thick. The formula uses the nominal (named) dimensions.

• $T_{\text{in}}$ = Nominal Thickness in inches (e.g., "2" for a 2x4)
• $W_{\text{in}}$ = Nominal Width in inches (e.g., "4" for a 2x4)
• $L_{\text{ft}}$ = Length in feet

Total Board Feet = $BF_{\text{per piece}} \times \text{Quantity}$

2. Framing Studs (On-Center)

This formula estimates the number of vertical studs needed for a wall of a given length.

Our calculator refines this by rounding up to the nearest whole number and adding an allowance for corners and intersections, typically 2-3 extra studs. $\text{Plates}$ are calculated by dividing the total wall length by the length of the lumber used for them, multiplied by the number of plates (e.g., one on bottom, two on top).

3. Lumber Weight

Weight is calculated using the actual dimensions (not nominal) to find the true volume, which is then multiplied by the wood's density.

• $\text{Volume}_{\text{ft}^3} = \left( \frac{T_{\text{actual in}} \times W_{\text{actual in}}}{144} \right) \times L_{\text{ft}} \times \text{Quantity}$
• $\text{Density} \approx G \times (1 + \frac{MC}{100}) \times 62.427 \text{ lb/ft}^3$
• $G$ = Specific Gravity of the wood (a measure of its density)
• $MC$ = Moisture Content as a percentage (e.g., 12% for kiln-dried)

Glossary of Variables

How It Works: A Step-by-Step Example

Let's estimate the cost and weight for a small project: 20 pieces of 2x6 lumber, each 12 feet long. The wood is Kiln-Dried Douglas Fir and costs $0.85 per board foot.

1. Select Calculator: We will use the 'Board Foot & Cost' and 'Lumber Weight' calculators.
2. Enter Dimensions:
   • Thickness (T): 2
   • Width (W): 6
   • Length (L): 12
   • Quantity: 20
3. Calculate Board Feet:
   • First, find the BF for one piece using the formula:
   • $BF_{\text{per piece}} = \frac{2 \times 6 \times 12}{12} = 12 \text{ BF}$
   • Now, find the total BF:
   • $\text{Total BF} = 12 \text{ BF/piece} \times 20 \text{ pieces} = 240 \text{ BF}$
4. Calculate Total Cost:
   • The cost is $0.85 per BF.
   • $\text{Total Cost} = 240 \text{ BF} \times \$0.85\text{/BF} = \$204.00$
5. Calculate Weight (Switch to Weight tab):
   • A nominal 2x6 is actually 1.5" x 5.5".
   • We select Douglas Fir (Kiln-Dried), which has a Specific Gravity (G) of ~0.43 and Moisture Content (MC) of 12%.
   • $\text{Density} = 0.43 \times (1 + \frac{12}{100}) \times 62.427 \approx 29.98 \text{ lb/ft}^3$
   • $\text{Volume (one piece)} = \left( \frac{1.5 \times 5.5}{144} \right) \times 12 \text{ ft} = 0.6875 \text{ ft}^3$
   • $\text{Weight (one piece)} = 0.6875 \text{ ft}^3 \times 29.98 \text{ lb/ft}^3 \approx 20.61 \text{ lbs}$
   • $\text{Total Weight} = 20.61 \text{ lbs/piece} \times 20 \text{ pieces} \approx 412.2 \text{ lbs}$

Frequently Asked Questions (FAQ)