Board Foot Calculator

What this calculator does

Thickness, width, length and quantity go in, plus both a per-board-foot price and a per-piece price. It returns board feet per piece, the total with waste, linear feet, the cost calculated each way, the implied price per board foot when buying by the piece, which method is cheaper, and roughly what the load weighs.

That implied-price comparison is the reason to use this rather than a one-line formula. Lumber is quoted in two incompatible units and the only way to compare a hardwood dealer against a lumberyard is to convert both.

What a board foot is

One board foot is the volume of a board one inch thick, twelve inches wide and one foot long — 144 cubic inches.

The working formula:

board feet = thickness(in) × width(in) × length(ft) ÷ 12

A 2×6 twelve feet long: 2 × 6 × 12 ÷ 12 = 12 board feet.

The division by twelve is doing unit reconciliation — two dimensions in inches and one in feet. If all three are in inches, divide by 144 instead. Both work; the first is easier at a lumber pile.

Nominal, not actual, and why that is fine

Here is the part that reliably confuses newcomers.

A 2×4 does not measure 2 by 4 inches. It measures 1.5 by 3.5, because it was sawn at full dimension green and then dried and surfaced down. A 2×6 is 1.5 by 5.5. A 1×8 is 0.75 by 7.25.

Board feet nonetheless use the nominal figures. A 2×4 counts as 2 by 4.

Which means board-foot volume overstates the actual wood in dimensional softwood by roughly a third. That sounds like a scandal and is not one: everybody in the trade knows it, prices are set with it in mind, and it has been the convention for over a century. The number is a trading unit, not a physical measurement.

For rough-sawn hardwood the distinction largely disappears, because rough lumber really is the dimension it is sold at — until you surface it.

Two pricing conventions, one comparison

Dimensional softwood — the 2×4s, 2×6s and 2×10s at a lumberyard — is sold by the piece. A 2×6×12 has a price, full stop. It is a commodity milled to a fixed size in enormous volume, so pricing it as an item is natural.

Hardwood and rough lumber are sold by the board foot, because they come in random widths and lengths straight off the log. There is no standard piece to price. You take what the boards are and pay for the volume.

The comparison problem is obvious once stated: you cannot tell whether $14 for a 2×6×12 is better than $1.35 per board foot without converting.

That 2×6×12 is 12 board feet. $14 ÷ 12 = $1.17 per board foot — cheaper than the $1.35 quote. The calculator does this both ways so the answer is visible rather than derived.

Same principle as the unit price calculator: convert to a common unit, then compare. It is the single most useful habit in buying anything.

Reading hardwood dimensions

Hardwood thickness is quoted in quarters of an inch, rough:

Called	Rough thickness	Typical surfaced
4/4	1 in	≈ 13/16 in
5/4	1¼ in	≈ 1‑1/16 in
6/4	1½ in	≈ 1‑5/16 in
8/4	2 in	≈ 1¾ in

Spoken as “four quarter,” “eight quarter.” You are billed on the rough thickness even when the dealer surfaces it for you, because the wood removed in surfacing came off your board.

Which is why buying rough and surfacing yourself is cheaper if you have a planer, and why the yield question — how much usable wood is in a board with sapwood, knots and wane — matters far more in hardwood than in softwood.

Waste, honestly

Ten percent is the default and it is right for straightforward dimensional work where you are cutting to length from stock lengths.

Push it higher when:

• Cutting to specific short lengths. Offcuts from a 12-foot board cut into 40-inch pieces are dead loss.
• Working with hardwood. Defects, sapwood and wane mean the usable yield from rough boards is often 70 to 85 percent of what you bought, before any cutting waste.
• Grain and colour matching matters. Furniture work rejects boards for reasons framing never would.
• You are hand-selecting for straightness. Crowned, twisted and split pieces get culled from your pile, not the yard’s.

Push it lower only with a cut list and a plan for the offcuts.

Weight, and your vehicle

Three pounds per board foot is a reasonable rule for kiln-dried softwood.

The default job on this page — forty 2×6×12s, 480 board feet plus waste — is roughly 1,600 pounds. That is beyond the payload of most half-ton pickups and well beyond what a trailer without brakes should carry.

Green lumber runs half again heavier. Dense hardwoods — oak, maple, hickory — run 4 to 5 pounds per board foot.

The trailer load calculator covers whether the vehicle can legally and safely take it, which is worth checking before the yard loads you rather than after.

What this leaves out

• Grade. Select Structural, No. 1, No. 2 and stud grade differ in strength and price, and structural spans depend on grade.
• Species. Douglas fir, southern yellow pine and spruce-pine-fir have different strengths and different prices.
• Moisture content, which affects weight, stability and how much the wood moves after installation.
• Treatment. Pressure-treated lumber carries a premium and different fastener requirements.
• Delivery, which for a load this size is often worth the fee.
• Yield on rough hardwood, discussed above.

For counting the pieces rather than pricing them, the stud wall calculator and deck boards calculator do the layout arithmetic.