Lumber Calculator

Framing a wall, decking a porch, or trimming a room and need to know how much lumber to buy — and what it'll cost? This calculator turns a board's dimensions and your quantity into board feet (how lumber is priced), linear feet (how trim is priced), coverage area, a waste allowance, and a total cost estimate.

Board feet — the unit lumber is sold in

Dimensional lumber is priced by the board foot: a piece of wood 1 inch thick, 12 inches wide, and 1 foot long. Any board converts to board feet with:

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

Multiply by quantity for the job total. Thickness and width use the nominal dimensions printed on the tag (a "2x6" is entered as 2 × 6), even though a finished/dressed 2x6 actually measures closer to 1.5" × 5.5" — nominal sizing is what lumber is bought and priced by.

Linear feet and coverage area

• Linear feet (length × quantity) is the unit trim, molding, and some fencing lumber is priced by instead of board feet — useful when your material list is quoted per linear foot rather than per board foot.
• Coverage area (width in feet × length × quantity) treats the boards as laid edge-to-edge, the way decking, siding, or subfloor boards are — a quick check against the square footage you're actually covering.

Waste allowance

The raw board-foot total assumes zero loss, which no real cut list achieves — defects, miscuts, and saw kerf all eat into usable length. The waste slider (default 10%, adjustable 0–30%) adds a percentage on top of the total board feet before pricing, so the number you buy already covers the material you'll lose to cutting.

Cost estimate

Enter a price per board foot and the calculator multiplies it by the waste-adjusted board-foot total. Leave the price blank to see quantities only — useful when you're still shopping around and don't have a quote yet.

How to use it

1. Enter the board's nominal thickness and width in inches, and its length in feet.
2. Enter how many boards you need.
3. Adjust the waste allowance slider if your project needs more or less than the 10% default.
4. Optionally enter a price per board foot to see an estimated total cost.
5. Results update automatically: board feet per board, total board feet, waste allowance, total board feet with waste, total linear feet, coverage area, and estimated cost.

FAQ

Why enter nominal dimensions instead of actual (dressed) dimensions? Because that's how lumber is priced and labeled at the yard — a "2x4" is sold and quoted as a 2x4 even though it's milled down to roughly 1.5" × 3.5". Using nominal sizing here keeps the board-foot total consistent with what you'll see on a price tag or invoice.

How much waste allowance should I use? 10% is a reasonable default for straightforward framing or decking. Increase it for projects with a lot of angled cuts, mitered joints, or figure-matched/select-grade material where more boards get rejected; a simple straight run (fence rails, blocking) can often use less.

Does this account for lumber grade, species, or treatment? No — those all affect price per board foot, which you supply directly. The calculator handles the geometry (board feet, linear feet, coverage) and multiplies by whatever price you enter, regardless of species or grade.

Can I use this for plywood or sheet goods? Not directly — sheet goods are priced per sheet or per square foot, not by board foot from thickness/width/length. This tool is for dimensional/solid-sawn lumber (studs, boards, trim, decking).

Privacy

All calculations run entirely in your browser — nothing you enter is sent to a server or stored.