Lumber Calculator

How to use the lumber calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Lumber — timber, if you are British — is priced two ways and confusing in both. A board foot is a volume — 144 cubic inches, or a piece one inch thick, twelve inches wide and a foot long — so the price per board foot has to be multiplied by thickness, width and length together. Buying by the linear foot instead means the price only makes sense for one specific section.

The catch that costs money is nominal size. A two-by-four has not measured two inches by four since planing became standard; it is one and a half by three and a half. Board feet are calculated from the nominal dimensions by convention, which means you pay for wood that was never delivered — an honest quirk of the trade rather than a swindle, and worth knowing when comparing a rough-sawn price against a planed one.

The stud count works the opposite way, from spacing rather than volume. A wall at 16-inch centres needs its length divided by the spacing, plus one for the closing stud, plus extra at corners and openings. Sixteen-inch centres suit standard sheet materials, which is why the spacing exists at all: an eight-foot sheet lands on a stud every time.

The waste allowance is not padding. Cuts, breakages, spillage and the offcuts around edges and openings are real losses on every job, and a second delivery costs far more than a spare bag or board.

Common uses

• Pricing a timber order quoted per board foot.
• Working out how many studs a partition wall needs.
• Comparing quotes given in different units.

Frequently asked questions

What is a board foot?

A volume of timber: 144 cubic inches, or one inch thick by twelve wide by a foot long. Thickness × width in inches × length in feet, divided by twelve.

Why is a 2×4 not two inches by four?

Because the nominal size is before planing; the finished piece is 1½ by 3½ inches. Board feet are still calculated from the nominal size by trade convention.

How many studs do I need for a wall?

The wall length divided by the spacing, plus one to close the end, plus extras at corners and either side of each opening. Sixteen-inch centres suit standard sheet sizes.