Count studs, joists or boards and get board feet, total linear feet and a lumber cost range.
Quick answer: Board feet equal thickness in inches times width in inches times length in feet, divided by 12. A 2x4 eight feet long is 2 times 4 times 8 divided by 12, or 5.33 board feet. Twenty of them come to 106.7 board feet and 160 linear feet; at $0.60 to $0.90 per board foot that is roughly $64 to $96 in lumber.
What do you have?
$
Hardwood commonly runs $4–$15 per board foot; construction softwood is often cheaper per board foot but sold by the piece.
Board feet
106.67
2 × 4 × 8.0 ft
Linear feet
160
20 pieces × 8 ft
The maths
Formulathickness × width × length ÷ 12
Your entry2 × 4 × 8 ÷ 12 × 20
Board feet106.67
Cost at $8.00/bf$853
Add 10% for cutting waste on framing, and remember that nominal sizes are larger than actual sizes — if a project specifies 2×6 actual dimensions, you are buying 5-1/2 in material.
Board feet are calculated from nominal dimensions — a 2×4 is 2 in by 4 in on paper, though it actually measures 1-1/2 in by 3-1/2 in. Softwood is usually priced per piece or per linear foot; hardwood is priced per board foot.
Core facts
Board feet
thickness × width × length ÷ 12
Nominal vs actual
A 2x4 is 1-1/2 by 3-1/2 in
Linear feet
pieces × length in feet
Stud spacing
16 in or 24 in on center
What is Lumber Calculator?
This calculator counts lumber. Enter how many pieces you need, their nominal size and their length, and it returns total linear feet, board feet and a cost line. Board feet is the trade's volume measure: thickness in inches times width in inches times length in feet, divided by 12. Lumber is sold by nominal size, so a 2x4 is actually 1-1/2 in by 3-1/2 in once it is surfaced, but board feet is calculated from the nominal figures — which is why a 2x4 eight feet long counts as 5.33 board feet rather than the 3.5 that its actual dimensions would give. Prices move with species and region, so treat the cost line as a check, not a quote.
Common uses for Lumber Calculator
Work out how many studs a wall needs at 16 in on center
Convert a framing takeoff into board feet for a lumber yard order
Compare the price of 8 ft and 10 ft boards for the same job
Total the linear feet of trim, decking or blocking you need
Estimate lumber cost before you drive to the yard
Nominal and actual sizes, side by side
Nominal size is the rough dimension before the board is planed. A 1x is 3/4 in thick, a 2x is 1-1/2 in thick, and widths shrink too: a 2x4 is 3-1/2 in wide, a 2x6 is 5-1/2 in, a 2x10 is 9-1/4 in. The calculator uses nominal figures for board feet, which is what yards bill against, while actual figures are what you measure when fitting. Keep the two separate and you will not order short.
Counting studs at 16 or 24 inches on center
Divide the wall length in inches by the spacing, then add one for the final stud. A 12 ft wall at 16 in on center is 144 divided by 16, plus one, which is ten studs. Add two for each corner and two for each window opening. Single top and bottom plates add two runs the length of the wall, and headers, sills and blocking are separate line items.
Why lumber prices move so much
Softwood framing is a commodity: prices track mills, freight and building season, and can shift by a third within a year. Treat any per-board-foot figure as a placeholder and get a quote against the actual list. Hardwoods are steadier but priced per board foot by species and grade, and the same board sold as FAS or as common can carry very different prices.
Frequently Asked Questions
How many studs do I need for a wall?
Studs sit 16 in or 24 in on center, so divide the wall length in inches by the spacing and add one for the final stud. A 16 ft wall at 16 in on center is 192 divided by 16, plus one, which is 13 studs. Add extra for corners, openings and blocking.
Why is a 2x4 not 2 in by 4 in?
Surfacing removes material. A kiln-dried 2x4 measures 1-1/2 in by 3-1/2 in, and a 2x10 measures 1-1/2 in by 9-1/4 in. Framing, sheathing and finish sizes are all planned around the actual dimensions, so measure a board from your yard before you cut anything to fit.
What is the difference between board feet and linear feet?
Linear feet counts length only: ten 8 ft boards are 80 linear feet whatever their width. Board feet counts volume, so it depends on thickness and width as well. Yards price framing lumber by the piece or the linear foot, and hardwoods by the board foot.
Does the cost estimate include waste?
No. It prices exactly the pieces you enter. Add 5 to 10 percent to your piece count for cutting waste, and more if the design has many angled cuts or short offcuts. Buy one extra board of any profile you cannot easily match later.