How to Calculate Board Feet
A board foot is a unit of timber volume used primarily in North America for measuring and pricing rough-sawn lumber and hardwoods. The formula is straightforward:
Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
Equivalent: Board Feet = (Thickness × Width × Length) ÷ 144 (all dimensions in inches)
For example, a board that is 1 inch thick, 6 inches wide and 8 feet long contains: (1 × 6 × 8) ÷ 12 = 4 board feet.
If you have 10 such boards, the total is 40 board feet (before any waste allowance).
Worked Example (Default Values)
Using the default inputs (imperial, 1 inch thick, 6 inches wide, 8 feet long, 10 pieces, 10% waste, $5.00 per board foot):
| Step | Calculation | Result |
|---|
| Board feet per piece | (1 × 6 × 8) ÷ 12 | 4.00 BF |
| Board feet for 10 pieces | 4.00 × 10 | 40.00 BF |
| 10% waste allowance | 40.00 × 1.10 | 44.00 BF |
| Total volume in cubic metres | 44.00 × 0.002359737 | 0.104 m³ |
| Estimated cost (incl. waste) | 44.00 × $5.00 | $220.00 |
Using Metric Dimensions
If your timber is measured in millimetres and metres (as is standard in New Zealand), convert to inches and feet first, or use the metric mode in this calculator. The conversion factors are:
- 1 inch = 25.4 mm, so thickness in inches = thickness in mm ÷ 25.4
- 1 foot = 0.3048 m, so length in feet = length in metres ÷ 0.3048
- Width in inches = width in mm ÷ 25.4
The metric mode in this calculator handles these conversions automatically.
Common Timber Sizes in Board Feet
| Thickness | Width | Length | Board Feet per Piece |
|---|
| 1 in | 4 in | 8 ft | 2.67 BF |
| 1 in | 6 in | 8 ft | 4.00 BF |
| 1 in | 8 in | 8 ft | 5.33 BF |
| 1 in | 6 in | 12 ft | 6.00 BF |
| 2 in | 4 in | 8 ft | 5.33 BF |
| 2 in | 6 in | 8 ft | 8.00 BF |
| 4 in | 4 in | 8 ft | 10.67 BF |
Board Feet vs Cubic Metres
In New Zealand, structural framing timber is typically sold by lineal metre or cubic metre, not board feet. However, hardwoods, specialty timbers and imported North American lumber (such as Douglas fir, cedar and redwood) are still priced in board feet. One board foot equals 0.002359737 cubic metres. To convert cubic metres to board feet, divide by 0.002359737 (or multiply by 423.776).
Waste Allowance
When purchasing timber for a project, it is good practice to add a waste allowance to account for off-cuts, defects, and end-trimming. A 10% allowance is typical for prepared (dressed) timber. For rough-sawn stock or where significant cutting is required, 15 to 20% is more appropriate. The waste percentage in this calculator is applied on top of the net quantity required.
Related Calculators
Method: Board foot formula: BF = (T″ × W″ × L') ÷ 12, where T is thickness in inches, W is width in inches and L is length in feet. Cubic metre conversion uses 1 BF = 0.002359737 m³ (exactly 144 cubic inches × (0.0254 m/in)³). Metric inputs are converted to inches and feet before applying the formula.
This calculator is for estimating purposes. Timber dimensions may vary due to dressing, moisture content and sawing tolerance. Always confirm quantities with your timber supplier before ordering. Prices are indicative only and vary by species, grade and supplier.
