Lumber Calculator (Board Feet & Cost)
Calculate board feet and total cost for dimensional lumber. Enter thickness, width, length, quantity and price per board foot for an instant, accurate result.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Lumber Calculator Works
This calculator converts the dimensions of dimensional lumber into board feet — the standard unit used to price and order wood — and then multiplies by your price per board foot to give a total material cost. Enter the thickness and width in inches, the length in feet, the quantity of pieces, and your price per board foot, and the result updates instantly.
Board feet are used because lumber comes in many different sizes; measuring everything by volume lets a mill or yard price a thin wide board and a thick narrow board on the same scale.
The Formula
For a single piece of lumber:
Board feet = (thickness in × width in × length ft) ÷ 12
Then scale up and add cost:
Total board feet = board feet per piece × quantity Total cost = total board feet × price per board foot
The divisor of 12 comes from the definition of a board foot (1 in × 12 in × 1 ft = 144 cubic inches). Because thickness and width are in inches but length is in feet, dividing the product by 12 converts it cleanly into board feet.
Worked Example
Suppose you need 10 pieces of 2 in × 6 in × 8 ft lumber at $3.50 per board foot:
- Board feet per piece = (2 × 6 × 8) ÷ 12 = 8 BF
- Total board feet = 8 × 10 = 80 BF
- Total cost = 80 × $3.50 = $280.00
If you switched to 2 × 8 × 10 ft boards instead, each piece would be (2 × 8 × 10) ÷ 12 = 13.33 BF, so 10 pieces would be 133.3 BF and cost about $466.67 at the same price.
Nominal vs. Actual Sizes
Most softwood is sold by its nominal size — the rough-cut dimension before planing. After surfacing, the actual size is smaller. Lumber yards still price by the nominal figure, so use nominal dimensions in this calculator unless you are working with rough, unsurfaced stock.
| Nominal size | Actual size (S4S) | Board feet per 8 ft |
|---|---|---|
| 2x4 | 1.5 × 3.5 in | 5.33 BF |
| 2x6 | 1.5 × 5.5 in | 8.00 BF |
| 2x8 | 1.5 × 7.25 in | 10.67 BF |
| 1x6 | 0.75 × 5.5 in | 4.00 BF |
Tips for Accurate Estimates
- Add a waste factor of 10–15% for offcuts, defects and mistakes — order a few extra board feet.
- Hardwoods are almost always sold by the board foot at the rough size; softwoods are often sold by the piece, so convert to board feet to compare prices fairly.
- Round up to whole boards when ordering, since you cannot buy a partial length.
Frequently asked questions
How do you calculate board feet?+
Multiply thickness (inches) × width (inches) × length (feet), then divide by 12. For one piece of 2 in × 6 in × 8 ft lumber: (2 × 6 × 8) ÷ 12 = 8 board feet. Multiply by the number of pieces for the total.
What is a board foot?+
A board foot is a unit of lumber volume equal to a board 1 inch thick, 12 inches wide and 12 inches long — that is 144 cubic inches. Lumber is priced and sold by the board foot, especially hardwoods and rough-sawn stock.
Do I use nominal or actual dimensions for board feet?+
Use nominal dimensions for pricing rough or unsurfaced lumber, since that is how mills quote it. For surfaced (S4S) boards, suppliers usually still bill by the nominal size, so a 2x6 is priced as 2 × 6 even though it actually measures about 1.5 × 5.5 inches.
How many board feet are in a 2x4x8?+
A 2 in × 4 in × 8 ft board contains (2 × 4 × 8) ÷ 12 = 5.33 board feet. At a price of $3.50 per board foot, that single board would cost about $18.67.
How do I estimate total lumber cost?+
First find your total board feet, then multiply by the price per board foot. For 10 pieces of 2x6x8 (8 BF each = 80 BF total) at $3.50/BF, the cost is 80 × $3.50 = $280. Add waste allowance and tax for a real-world budget.