Board Foot Calculator
A board foot is one inch thick, twelve inches wide and one foot long, and the formula for it is on every lumber site. What is not on them is that the number is calculated from the rough or nominal size, not the board in front of you. A 4/4 board surfaced to thirteen sixteenths is billed as a full inch. A 2×4 that measures an inch and a half by three and a half is counted as two by four. This calculator gives the board foot figure the yard will charge you for, and next to it the wood that will actually arrive on the truck.
- Board feet
- 40.00 bf 1" × 6" × 8 ft ÷ 12 = 4.00 bf per piece, × 10 pieces
- Cost at this price
- $260.00 40.00 bf × $6.50
- Wood you actually receive
- 32.50 bf Surfaced to 0.8125" from a 1" rough thickness. Hardwood is billed at the rough thickness — the planer shavings are yours to pay for.
- What the difference costs
- $48.75 7.50 bf of the order is thickness and width removed at the mill. This is normal and correct billing practice — it is not an error, but it is a real cost most estimates omit.
- Linear feet
- 80 ft Priced by the linear foot instead, the same order works out to $3.25 per foot. Yards quote one or the other, rarely both.
- Quarter notation
- 4/4 1" rough is written 4/4 and spoken "4 quarter". A yard asking what thickness you want expects this answer, not a decimal.
Board feet measure volume, not the board
The unit is straightforward: thickness in inches times width in inches times length in feet, divided by twelve. One board foot is 144 cubic inches of wood.
The complication is which dimensions go into the formula. For hardwood the answer is the rough thickness before surfacing, expressed in quarters of an inch — 4/4 for one inch, 5/4 for an inch and a quarter, 8/4 for two inches. Once that board is surfaced on two sides it measures thirteen sixteenths, but it is still sold as 4/4 and still billed at a full inch.
For softwood dimensional lumber the answer is the nominal size. A 2×4 is billed as two inches by four inches even though it leaves the planer at an inch and a half by three and a half. That is a third less wood than the invoice describes.
None of this is a scam, and every yard in the country works this way. It is simply a pricing convention that predates modern milling. But an estimate that treats board feet as actual volume will be wrong by between nineteen and thirty-four percent depending on the stock, which is more than most jobs have in margin.
Quarter sizes, and why the yard asks in them
Hardwood thickness is spoken in quarters of an inch. Four quarter is one inch, five quarter is an inch and a quarter, eight quarter is two inches. Ask for a one inch board and you will get 4/4, which finishes at thirteen sixteenths — thinner than the inch you asked for.
This matters when a design needs a specific finished thickness. A three quarter inch tabletop comes from 4/4 stock. A finished inch needs 5/4. Ordering 4/4 for a project drawn at one inch is the most common hardwood ordering mistake, and it is discovered at the planer rather than at the yard.
Rough sawn stock is thicker than its quarter designation, usually by a sixteenth or so, because it is measured wet and green. If you are surfacing your own material you have that margin to work with; if you are buying S2S you do not.
Anything thinner than one inch is still billed as 4/4. There is no discount for ordering a half inch board, because the mill cut it from a 4/4 blank.
Board feet against linear feet
Two boards can have identical board footage and cost very different amounts to use, because board feet ignore width.
A yard quoting by the board foot charges the same for eight feet of six inch stock as for four feet of twelve inch stock. If your project needs long pieces, the narrow boards are worse value even at the same price, because you will be joining where the wide board would have been one piece.
Softwood is usually quoted by the linear foot or by the piece, hardwood almost always by the board foot. When comparing suppliers, convert both to the same unit — this calculator gives the linear foot equivalent so a board foot price can be compared against a piece price directly.
Wide boards also carry a premium in most hardwood yards beyond a certain width, typically ten or twelve inches, because they come from larger and scarcer logs. That premium does not appear in the board foot arithmetic; ask about it before assuming a wide board and a narrow one price alike.
What this is based on
- Board foot definition — thickness × width × length ÷ 12
- Standard hardwood quarter thickness notation and S2S surfacing allowances
- Nominal versus actual dimensions for surfaced softwood lumber
A pricing and quantity estimate. Yards differ in how they measure width on irregular boards, how they handle over-length stock, and whether wide boards carry a premium. Confirm the measuring convention with your supplier before ordering a large quantity.
Frequently asked questions
What is a board foot?
A volume of wood one inch thick, twelve inches wide and one foot long — 144 cubic inches. Thickness in inches times width in inches times length in feet, divided by twelve.
Why does a 2×4 count as 2 by 4 when it measures 1.5 by 3.5?
Board feet for softwood dimensional lumber are calculated on the nominal size, which describes the rough sawn dimension before drying and planing. The convention is universal, so it is fair between suppliers, but it means the billed volume is about a third larger than the wood delivered.
What does 4/4 mean?
Four quarters of an inch, so one inch of rough thickness. It is pronounced "four quarter". Surfaced on two sides it finishes at thirteen sixteenths, which is why a project drawn at a full inch needs 5/4 stock.
Is thinner stock cheaper per board foot?
No. Anything under one inch is billed as 4/4 because the mill cut it from a 4/4 blank. Half inch stock costs the same per board foot as one inch stock and gives you half the wood.
Should I buy rough or surfaced?
Rough is cheaper per board foot and gives you the full thickness to work with, but you need a planer and jointer and you will lose a portion of it anyway. Surfaced costs more and arrives ready to use. For one or two boards, buy surfaced; for a large order with machines available, rough usually wins.