The board foot formula in three versions
A board foot (BF) is a volume: 1 in × 12 in × 12 in = 144 cubic inches. Which version of the formula you use depends on the units of the length:
- All three dimensions in inches:
BF = T × W × L ÷ 144 - Thickness and width in inches, length in feet:
BF = T × W × L ÷ 12 - For a whole line of identical pieces:
BF = quantity × T × W × L ÷ 12
Twelve board feet make one cubic foot, and one board foot is about 0.00236 cubic metres.
Nominal size or actual size?
Softwood dimension lumber is counted at its nominal size. A 2x4 actually measures about 1-1/2 × 3-1/2 inches after drying and planing, but it counts as 2 × 4 in the board foot formula. Hardwood is sold by thickness in quarters of an inch, 4/4 (1 inch), 5/4, 8/4 (2 inches), measured rough before surfacing, and many dealers count boards thinner than 1 inch as 1 inch. When you compare quotes, check which convention each supplier uses, because the same stack can be a different number of board feet.
Step by step: a lumber list in Excel
Put each item on a row with its quantity, thickness, width and length, then one formula per line:
=B2*C2*D2*E2/12
For the 40 studs that is 40 × 2 × 4 × 8 ÷ 12 = 213.33 BF. The twelve 16 ft 2x6 plates are 192 BF, the ten 12 ft 2x10 joists 200 BF, the four 14 ft 2x12 headers 112 BF and the four 10 ft 4x4 posts 53.33 BF. =SUM(F2:F6) gives 770.67 board feet for the whole list.
Worked example: board feet and cost of a framing order
Quantities, sizes, the price per MBF, the tax rate and the delivery charge are yellow. Column F calculates the board feet of each line and the order total below.
| A | B | C | D | E | F | |
|---|---|---|---|---|---|---|
| 1 | Item | Qty | Thick (in) | Width (in) | Length (ft) | Board feet |
| 2 | 2x4 studs | 40 | 2 | 4 | 8 | 213.33 |
| 3 | 2x6 plates | 12 | 2 | 6 | 16 | 192.00 |
| 4 | 2x10 joists | 10 | 2 | 10 | 12 | 200.00 |
| 5 | 2x12 headers | 4 | 2 | 12 | 14 | 112.00 |
| 6 | 4x4 posts | 4 | 4 | 4 | 10 | 53.33 |
| 7 | Total board feet | 770.67 | ||||
| 8 | Price per MBF (1,000 board feet, $) | 850.00 | ||||
| 9 | Price per board foot ($) | 0.85 | ||||
| 10 | Lumber cost ($) | 655.07 | ||||
| 11 | Sales tax rate | 7.0% | ||||
| 12 | Delivery charge ($) | 75.00 | ||||
| 13 | Order total ($) | 775.92 | ||||
| 14 | One 2x4 × 8 ft: board feet per piece | 5.33 | ||||
| 15 | One 2x4 × 8 ft: price per piece ($) | 4.53 | ||||
- F2
=B2*C2*D2*E2/12Board feet of the line - F7
=SUM(F2:F6)Total board feet - F9
=F8/1000Price per board foot - F13
=F10*(1+F11)+F12Order total with tax and delivery - F14
=C2*D2*E2/12Board feet of one 2x4 × 8 ft
Illustrative prices, tax rate and job. Local building codes and the approved drawings decide sizes and spacing. Tabellab is not affiliated with any code body or lumber association.
From board feet to price: per BF and per MBF
Lumber yards and mills often quote per MBF, a thousand board feet. $850 per MBF is $0.85 per board foot. The lumber cost is 770.67 × $0.85 = $655.07. With 7% sales tax and a $75 delivery charge the order comes to $775.92.
To compare a board foot price with a price per piece, multiply: one 2x4 × 8 ft is 5.33 BF × $0.85 = $4.53. Retail stores usually price dimension lumber per piece and hardwood per board foot, so this conversion is the quickest way to see which offer is cheaper.
Quick reference: common sizes
- 2x4 × 8 ft = 5.33 BF
- 2x6 × 8 ft = 8 BF
- 2x10 × 12 ft = 20 BF
- 4x4 × 10 ft = 13.33 BF
- 1x6 × 8 ft = 4 BF
- 8/4 hardwood, 6 in wide × 8 ft = 8 BF
A useful shortcut: for a 1-inch board 12 inches wide, board feet equal the length in feet. For a 2x6, board feet equal the length.
Allow for waste before you order
The formula gives the volume you need, not the volume you should buy. Hardwood projects often add 15 to 30% for defects, grain matching and offcuts, and framing takeoffs add a smaller allowance for bad pieces and cuts. Once the materials are priced, labour, overhead and markup turn the takeoff into a job price, see markup vs margin.
Common mistakes
- Dividing by 144 when the length is in feet. ÷ 144 is for inches × inches × inches. With the length in feet, divide by 12.
- Using actual instead of nominal sizes. A 2x4 counts as 2 × 4 for softwood board feet, even though it measures 1-1/2 × 3-1/2.
- Forgetting the quantity. The formula gives the board feet of one piece. Multiply by the number of pieces on the line.
- Confusing linear feet with board feet. Linear feet measure length only. Board feet measure volume, so a 2x12 has six times the board feet of a 1x4 of the same length.
- Mixing up price per MBF and per BF. $850 per MBF is $0.85 per board foot, not $850.
- Ordering exactly the calculated volume. Add a waste allowance for defects, cuts and offcuts.
Frequently asked questions
How many board feet are in a 2x4x8?
5.33 board feet: 2 × 4 × 8 ÷ 12. Board feet use the nominal size, so the actual 1-1/2 × 3-1/2 inch section does not change the count.
How do you calculate board feet?
Multiply the thickness in inches by the width in inches by the length in feet and divide by 12. If all three dimensions are in inches, divide by 144 instead.
What does MBF mean in lumber pricing?
MBF means a thousand board feet. A price of $850 per MBF equals $0.85 per board foot.
How many board feet are in a cubic foot?
Twelve. A cubic foot is 1,728 cubic inches and a board foot is 144 cubic inches.