Board Foot Calculator — lumber volume, cost and quantity

The board foot calculator above converts lumber dimensions into the unit the timber trade actually sells in. A board foot is a volume — 144 cubic inches — and it exists because timber is a three-dimensional commodity that comes in wildly varying widths and lengths, so pricing it per piece or per linear foot would make comparison impossible. Once everything is in board feet, a wide short board and a narrow long one can be priced against each other honestly.

Arb Digital publishes this alongside a free set of construction and woodworking tools. The arithmetic is a single multiplication and a division by 144, and yet board foot calculations go wrong constantly — almost always because of the difference between the size printed on the ticket and the size you can measure with a tape.

What This Board Foot Calculator Does

It multiplies thickness by width by length, normalises everything to inches, divides by 144, and multiplies by the number of pieces. It shows the board feet per piece and the total, applies a waste factor, converts the result to cubic feet and cubic metres, and prices the order at your rate per board foot. It also applies the minimum charged thickness that most hardwood yards use on thin stock, which is a real line on a real invoice and is frequently missing from calculations done at home.

This is a lumber trade-unit tool, and that is what separates it from the neighbours. The cubic yard calculator converts bulk volume for aggregate and concrete, which is a different unit for a different commodity. The material weight calculator turns a volume into a mass using density. This page does neither — it produces the trade volume a timber merchant invoices against. If you are counting pieces for a specific structure rather than pricing a pile of stock, the decking calculator and wall framing calculator count members directly.

How to Use It

1. Decide whether you are working in nominal or actual sizes. This is the choice that determines whether your answer matches the invoice. Read the next section before picking.
2. Enter thickness and width in inches. Hardwood quarters convert directly — 4/4 is 1 inch, 5/4 is 1.25, 6/4 is 1.5, 8/4 is 2.
3. Enter the length, and tell the tool whether it is in feet or inches. Both are common, and mixing them up gives an answer wrong by a factor of twelve.
4. Set the piece count and price. Price is per board foot, which is how hardwood is sold. Softwood dimensional lumber is usually priced per piece.
5. Add a waste factor. Rough hardwood needs considerably more than surfaced stock, because you are buying defects along with the timber.

The Formula and How It Is Calculated

One board foot is 144 cubic inches. So:

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

Because lengths are usually quoted in feet, the more convenient form is:

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

Both are the same equation — the second has already divided one dimension by twelve to convert feet to inches.

A worked example. Ten pieces of 2x8, each 12 ft long, figured on nominal sizes: 2 × 8 × 12 ÷ 12 = 16 board feet per piece, so 160 board feet in total. At $4.50 per board foot that is $720. Now figure the same order on actual surfaced dimensions of 1.5 by 7.25 inches: 1.5 × 7.25 × 12 ÷ 12 = 10.875 board feet per piece, or 108.75 total. That is 32 percent less timber for the same ten sticks, and the difference is not an error in either calculation — it is the difference between what the trade counts and what you receive.

Nominal Versus Actual: The Whole Problem in One Section

Softwood dimensional lumber is named by the size it was before it was dried and surfaced. A piece called 2x4 is 1.5 by 3.5 inches. A 2x8 is 1.5 by 7.25. A 1x6 is 0.75 by 5.5. These are not approximations — they are standardised sizes set out in the American Softwood Lumber Standard, developed by the American Lumber Standard Committee and published through the NIST Voluntary Product Standards Program under the Department of Commerce. That standard is what makes a 2x4 the same dimension in every yard in the country.

The trade convention is that softwood board feet are figured from the nominal size. A 2x4 is counted as 2 by 4 even though it measures 1.5 by 3.5, because that is how the tally and the price list are built. Structural design, on the other hand, uses the actual dimensions, because the wood that carries load is the wood that is there — the design values and section properties in the American Wood Council's National Design Specification for Wood Construction are all based on dressed dimensions.

Hardwood works differently again. It is sold by rough thickness in quarters of an inch, with the width and length measured as they come — hardwood boards are rarely uniform. The board footage is calculated on the rough dimensions before surfacing, so when you have a 4/4 board surfaced to 13/16 inch, you paid for the full inch. That is not sharp practice; it is the material removed to make the board flat, and it is the reason the waste factor on this page defaults higher than it would for construction lumber.

Why the Waste Factor Matters More for Hardwood

With dimensional softwood you can usually order close to what you need, because the boards are straight, uniform and defect-graded to a predictable standard. Rough hardwood is different. You are buying boards of random width and length that contain knots, checks, sapwood, wane and often a degree of cup or twist that has to be planed out.

Practical guidance from furniture makers: budget 20 to 30 percent above the finished board footage for straightforward work in a clear grade, and considerably more where you are matching grain or colour across a panel, working with figured stock, or cutting a lot of short parts from long boards. The hidden cost is defect placement — a board with a knot in the middle may be useless for a 40 inch part even though it has 60 inches of clear timber in it, split into two 20 inch pieces.

The other quiet cost is thicknessing. A 4/4 board surfaced two sides comes out around 13/16 inch, which is fine until you need a finished thickness of 7/8. Then you have to buy 5/4 and lose a quarter inch, paying for 25 percent more timber to gain a sixteenth. Plan the thicknesses of every part before you buy, not after.

Board Feet, Linear Feet and Square Feet Are Not Interchangeable

Three units get confused constantly, and they measure different things.

Linear feet measures length only. It is how trim, moulding and dimensional lumber of a known section are often sold, and it says nothing about how much timber you get unless the section is fixed.

Square feet measures area, which is what sheet goods and flooring are sold in. A board's surface measure — its width times its length — is an area, and it is a component of the board foot calculation but not the answer.

Board feet measures volume. It is the only one of the three that tells you how much wood is actually in the pile, and it is the only one that lets you compare a 6 inch wide board with a 12 inch wide one on price.

Converting between them requires the missing dimension. Linear feet to board feet needs the thickness and width. Square feet of flooring to board feet needs the thickness — and the two will not agree anyway, because flooring is sold on coverage after milling while the board foot is the volume before it. For sheet goods, count sheets rather than board feet; the plywood sheet calculator does that directly.

Metric Timber and Why Cubic Metres Are Cleaner

Outside North America, timber is sold by the cubic metre, and the arithmetic is simply thickness times width times length in metres. One cubic metre is about 424 board feet, and this tool reports both so you can compare a quote in one system with a quote in the other.

The metric system also sidesteps the nominal-versus-actual problem to a large extent, because European and Australian timber is generally sold at its actual finished dimension, with a separate term for sawn rough sizes. A 45 by 95 mm piece is 45 by 95 mm. Where it does not sidestep it is in "target sizes" for planed timber, which are stated as a finished dimension with a permitted tolerance, and in the difference between sawn and regularised stock. When comparing quotes internationally, always confirm whether the quoted dimension is sawn or finished before converting anything.

Common Mistakes to Avoid

• Mixing nominal and actual sizes in one order — figure the whole tally one way or the other, and know which way your supplier is quoting.
• Dividing by 12 when the length is in inches — the divisor is 12 for a length in feet and 144 for a length in inches, and using the wrong one is off by twelvefold.
• Forgetting the minimum charged thickness — many hardwood yards bill thin stock at a full inch, which quietly increases the invoice above your calculation.
• Treating board feet as square feet — one is a volume and the other an area, and they only coincide by accident on nominal one-inch stock.
• Ordering the finished board footage — rough hardwood loses material to defects, squaring up and thicknessing, so the purchase quantity must be meaningfully higher.

Related Free Tools From Arb Digital

Pair this with the cubic yard calculator for bulk volume, the material weight calculator for turning volume into mass, the plywood sheet calculator for sheet goods, the decking calculator for deck boards and the wall framing calculator for stud counts. The board and batten calculator handles vertical cladding layouts. The full free online tools hub lists every calculator we publish.

Frequently Asked Questions

This tool produces material and cost estimates only. Grading rules, dimensional standards and pricing conventions vary between suppliers and between countries, and any order should be confirmed against your supplier's own tally before purchase.