Woodworking guide
Board Foot Chart: How to Calculate Board Feet and Price a Lumber Order
Board feet explained: thickness × width × length ÷ 12, what 4/4 and 8/4 mean, a chart of common board sizes with example prices, and how to add waste.
Quick answer
A board foot is 144 cubic inches of wood: a piece 1 in thick, 12 in wide and 12 in long. One 4/4 board that is 6 in wide and 8 ft long is 1 × 6 × 8 ÷ 12 = 4 board feet. Ten of them are 40 board feet, or 46 with a 15% allowance for defects and offcuts. At an example price of $8 per board foot that is $320 for the boards and $368 with the allowance.
Formula
board feet = thickness (in) × width (in) × length (ft) ÷ 12 | quarters: 4/4 = 1 in, 8/4 = 2 in | to buy = board feet × (1 + waste %)
Accuracy
Reference table
Search by name or sort by any column. Each row links to the matching calculator.
12 of 12 rows · sorted by rough thickness
| Calculator | |||||
|---|---|---|---|---|---|
| 4/4 (1 in) | 4 in | 8 ft | 2.67 | $21.33 | Board foot calculator |
| 4/4 (1 in) | 6 in | 8 ft | 4.00 | $32.00 | Board foot calculator |
| 4/4 (1 in) | 8 in | 8 ft | 5.33 | $42.67 | Board foot calculator |
| 4/4 (1 in) | 6 in | 10 ft | 5.00 | $40.00 | Board foot calculator |
| 4/4 (1 in) | 8 in | 10 ft | 6.67 | $53.33 | Board foot calculator |
| 4/4 (1 in) | 12 in | 8 ft | 8.00 | $64.00 | Board foot calculator |
| 5/4 (1.25 in) | 6 in | 8 ft | 5.00 | $40.00 | Board foot calculator |
| 6/4 (1.5 in) | 6 in | 8 ft | 6.00 | $48.00 | Board foot calculator |
| 8/4 (2 in) | 6 in | 8 ft | 8.00 | $64.00 | Board foot calculator |
| 8/4 (2 in) | 8 in | 8 ft | 10.67 | $85.33 | Board foot calculator |
| 8/4 (2 in) | 8 in | 10 ft | 13.33 | $106.67 | Board foot calculator |
| 12/4 (3 in) | 8 in | 8 ft | 16.00 | $128.00 | Board foot calculator |
How it works
The formula: thickness × width × length ÷ 12
A board foot is a volume of 144 cubic inches, the size of a board 1 in thick, 12 in wide and 12 in long. With thickness and width in inches and length in feet, board feet = thickness × width × length ÷ 12. The 12 turns feet into inches, and the same sum in all inches is thickness × width × length ÷ 144. A 4/4 board 6 in wide and 8 ft long gives 1 × 6 × 8 ÷ 12 = 4 board feet; check it the long way, 1 × 6 × 96 ÷ 144 = 4. In metric, one board foot is about 0.00236 cubic metres, so the 40 board feet in the example is about 0.094 m³. Doubling any one dimension doubles the board feet, which is why an 8/4 board is priced at twice the board feet of a 4/4 board of the same width and length.
Quarters: why 4/4 is one inch and 8/4 is two
Hardwood is sold by its rough thickness in quarters of an inch: 4/4 is 1 in, 5/4 is 1 1/4 in, 6/4 is 1 1/2 in, 8/4 is 2 in and 12/4 is 3 in. Board feet are worked out on that rough size, so the surfaced board you take home is thinner than the number you paid for. As a typical figure, a 4/4 board planes down to somewhere around 3/4 in, but it varies by mill and by how much cleanup the board needs, so ask your supplier what thickness to expect. If your project needs a finished thickness, buy the next quarter up. The chart on this page shows the board feet in each common size, worked out by the calculator below.
Waste, price per board foot and what a board costs
Cost is board feet times the price per board foot. For the default example, 40 board feet at $8 is $320. Then add an allowance for end checks, knots, sapwood, warp and saw kerf: multiply the board feet by (1 + waste). A typical hardwood allowance is 10% to 25%, and rustic or narrow stock can need more. At 15%, 40 board feet becomes 46 and the cost $368. Many yards sell random widths and lengths, so measure the boards you are handed or ask for a tally sheet instead of trusting a nominal size. Softwood construction lumber is usually priced per piece or per linear foot rather than per board foot, so this arithmetic mostly applies to hardwood and specialty stock.
Work it out
Change the inputs to work out your own numbers. Each step of the working is shown with the answer.
Your measurements
Enter one board size and how many you need. Everything updates as you type.
One board
4/4 is 1 in thick. Hardwood yards price on this rough thickness, not the planed one.
Measure the narrowest point of the board, or the width the yard quotes.
How many, and the price
Boards of the size above. For a mix of sizes, run each size and add the totals.
15% is a common starting point for hardwood. Allow more for knotty stock or a tight grain match.
From the yard's price list. Leave at 0 if you only need the board feet.
Results
Board feet to buy
bd ft
= 10 boards, 4/4 × 6" × 8 ft
40 board feet of boards plus 15% extra, about $368.00 at $8.00 per board foot.
- One board
- 4bd ft
- 1" × 6" × 8 ft
- Before waste
- 40bd ft
- 0.0944 m³ of wood
- Cost
- $368.00
- $320.00 before waste
How this was calculated
Board feet, waste and cost, with your numbers.
How this was calculated
Board feet, waste and cost, with your numbers.
Step 1: Board feet in one board
thickness (in) × width (in) × length (ft) ÷ 12
= 1 × 6 × 8 ÷ 12
= 4 board feetOne board foot is a piece 1 inch thick, 12 inches wide and 12 inches long (144 cubic inches). Dividing by 12 instead of 144 works because the length is in feet.
Step 2: Multiply by the number of boards
board feet per board × boards
= 4 × 10
= 40 board feetThis is what the boards measure, before any waste.
Step 3: Add the waste allowance
board feet × (1 + waste)
= 40 × 1.15
= 46 board feet to buyExtra for defects, knots, snipe and cutting mistakes. The percentage is your choice; 15% is a common starting point for hardwood.
Step 4: Cost
board feet to buy × price per board foot
= 46 × $8
= $368.00Without the waste allowance the boards you need come to $320.00. Rough lumber is priced on its rough thickness, so measure the thickness the yard quotes (4/4, 8/4), not the planed thickness.
Troubleshooting
What usually goes wrong, how to check for it, and how to prevent it.
The invoice shows more board feet than your cut list
- Cause
- The supplier prices on rough size, rounds widths or lengths up, or counts the whole board rather than the part you will use
- How to check
- Work out thickness × width × length ÷ 12 for each board on the invoice and compare it with the line total
- Prevention
- Ask which size the supplier prices on and whether widths and lengths are rounded, and ask for a tally of every board
You run out of boards before the project is done
- Cause
- No allowance was added for defects, kerf and offcuts, or the wide boards you planned on were all narrower
- How to check
- Board feet needed with no waste is close to the board feet bought
- Prevention
- Add 10% to 25% for hardwood, buy all the boards from one lot so the colour matches, and lay out the cuts before you buy
Your total is wildly different from the quote
- Cause
- Length was entered in inches instead of feet, or the quarters number was entered as inches
- How to check
- The answer is out by a factor of 12 or 4 compared with a quick 1 × 6 × 8 ÷ 12 = 4 check
- Prevention
- Enter length in feet and thickness in quarters (4 for 4/4), and test the method on one board you can add up in your head
Common questions
How many board feet are in a 4/4 board that is 6 inches wide and 8 feet long?
Four. Thickness 1 in × width 6 in × length 8 ft ÷ 12 = 4 board feet. Ten of those boards are 40 board feet before waste.
What do 4/4 and 8/4 mean on hardwood?
They are rough thicknesses in quarters of an inch: 4/4 is 1 in, 5/4 is 1 1/4 in, 6/4 is 1 1/2 in, 8/4 is 2 in. The finished board is thinner after planing, so buy the next quarter up if you need a particular finished thickness.
Do I pay for the rough size or the planed size?
Hardwood is normally priced on its rough thickness and the width and length of the board as sold, not on what is left after surfacing. Suppliers differ, so ask how they measure before you order.
How much extra lumber should I buy?
A typical allowance for hardwood is 10% to 25% over the board feet your cut list needs, to cover defects, kerf and offcuts. Use the higher end for rustic or narrow boards and for projects where grain and colour have to match.