Board Feet Explained: How Lumber Is Measured and Priced

Two ways to sell a plank

Walk into a timber yard and you meet two different worlds. Softwood studs — your 2x4s and 2x6s — are stacked and sold by the piece or by length. Hardwood, by contrast, is sold by the board foot, a unit that confuses newcomers because it sounds like a length but is actually a volume. Understanding why — and decoding the odd fact that a 2x4 isn't 2 inches by 4 — turns buying wood from guesswork into arithmetic.

What a board foot actually is

A board foot is 144 cubic inches of wood — specifically, the volume of a board one inch thick, twelve inches wide, and twelve inches long. It's a measure of how much wood you're getting, which is exactly what you want when boards come in wildly different thicknesses and widths.

The formula is:

Board feet = (thickness × width × length in inches) ÷ 144

Or, if the length is in feet (as it usually is), the tidier version:

Board feet = (thickness × width in inches × length in feet) ÷ 12

A board 2 inches thick, 6 inches wide, and 8 feet long works out to (2 × 6 × 8) ÷ 12 = 8 board feet. The Board Foot Calculator handles this for a single board or a whole batch, and can price it too.

Why board feet, and not just length?

Length alone — "linear feet" or "running feet" — tells you nothing about how much wood is in a board. A 10-foot length of thin, narrow trim and a 10-foot length of thick, wide plank are both "10 linear feet," yet one contains a fraction of the material of the other.

Board feet fix this by measuring volume, so a thick wide board correctly costs more than a thin narrow one of the same length. That's why hardwood, which comes in irregular, varied sizes, is almost always priced per board foot. Dimensional softwood (studs, joists) is uniform enough that selling by the piece or linear foot is simpler. Knowing which unit you're buying in prevents some expensive misunderstandings.

The "2x4 isn't a 2x4" mystery

This one catches every beginner. Buy a 2x4 and measure it: you'll find it's roughly 1.5 inches by 3.5 inches, not 2 by 4. You weren't shortchanged — those are nominal versus actual dimensions.

The nominal size (2x4) is the rough-sawn dimension before the lumber is dried and planed smooth. Drying shrinks it; planing removes more to give clean, consistent faces. The finished board ends up smaller, but the industry kept the original nominal name for ordering convenience. The practical takeaway: order by nominal size, but build to actual size. Design a shelf assuming a "2x8" is really 8 inches wide and your joints won't fit.

For board-foot pricing, note that the convention uses the nominal thickness and width — a quirk worth knowing when you reconcile what you paid against what you measured.

Costing a project

Once you have total board feet, cost is a single multiplication:

cost = board feet × price per board foot.

Hardwood might run several dollars per board foot depending on species and grade, so a project's lumber bill adds up fast. And board feet is only the material figure — real projects need extra for defects you cut around, mistakes, and offcuts. For furniture-grade work, 15–20% extra is a sensible allowance; rough construction can get away with less. The Board Foot Calculator lets you enter a price per board foot to see the running cost as you plan.

A quick buying checklist

• Decide whether you're buying by board foot (hardwood) or by the piece / linear foot (dimensional softwood).
• Order by nominal size but design and cut to actual size.
• Add a waste allowance — more for fine work, less for rough.
• For hardwood, inspect for defects; you pay by volume, so knots and splits you'll cut out are wasted money.

Running the numbers

Enter thickness, width, length, and quantity into the Board Foot Calculator for total board feet and cost. If your build also involves sheet goods or framing areas, the Area Calculator and Volume Calculator help with those.

Sources

1. US Forest Products Laboratory. Wood Handbook — Wood as an Engineering Material.
2. National Hardwood Lumber Association (NHLA). Rules for the Measurement and Inspection of Hardwood.
3. American Softwood Lumber Standard (PS 20) — nominal vs actual dimension conventions.

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This article is for general informational purposes.