Board Foot Calculator

A board foot is a unit of lumber volume: one board foot equals a piece of wood 1 inch thick, 12 inches wide, and 12 inches long. Enter your lumber’s dimensions below to calculate board feet and estimate cost. The formula is simple; the part that trips people up is which dimensions to use.

Nominal size (quick-select)

2x42x62x82x102x121x41x6Custom

Thickness (in, nominal)

Width (in, nominal)

Length (ft)

Quantity (pieces)

Waste (%)

Board feet per piece

5.33 bd ft

Total board feet

5.33 bd ft

Total with waste

5.87 bd ft

Uses nominal dimensions (not the smaller actual/finished size). Includes a 10% waste buffer across 1 piece.

The Formula

Board Feet = (Thickness in. × Width in. × Length ft.) ÷ 12

That’s it. The only real question is what numbers to plug in, and that’s where nominal vs. actual dimensions comes in.

The Trap: Nominal vs. Actual Dimensions

A “2×4” isn’t actually 2 inches by 4 inches. When lumber is first cut at the sawmill, it genuinely is that size, but drying and planing on all four sides shrinks it down. The finished board you buy at the lumberyard measures 1½ × 3½ inches.

Here’s the part that confuses people: board foot calculations for standard dimensional lumber use the nominal size (2×4), not the actual size (1½×3½). That’s because lumber is priced and tallied at the mill based on the rough-cut nominal dimension, before the shrinkage happens. Pricing has stuck with that convention ever since.

Nominal Size	Actual Size
1×4	¾ × 3½ in
1×6	¾ × 5½ in
2×4	1½ × 3½ in
2×6	1½ × 5½ in
2×8	1½ × 7¼ in
2×10	1½ × 9¼ in
2×12	1½ × 11¼ in

If you calculate board feet from the actual dimensions instead of nominal, you’ll underestimate every piece, and your total won’t match the supplier’s invoice.

Worked Example

A 2×4 that’s 8 feet long, using nominal dimensions:

(2 × 4 × 8) ÷ 12 = 5.33 board feet

Quick reference for common 8-foot boards (nominal dimensions, at 8 ft length):

Size	Board Feet (8 ft)
2×4	5.33
2×6	8.00
2×8	10.67
2×10	13.33
2×12	16.00

For a full project: say you need 8 pieces of 2×6, each 10 feet long.

Per piece: (2 × 6 × 10) ÷ 12 = 10 board feet
Total: 10 × 8 = 80 board feet
Add 10% for waste and off-cuts: 80 × 1.10 = 88 board feet

One More Wrinkle: Hardwood

If you’re buying hardwood rather than dimensional softwood framing lumber, thickness is quoted in quarters instead of whole inches: 4/4 = 1 inch, 5/4 = 1¼ inch, 6/4 = 1½ inch, 8/4 = 2 inches. Most hardwood yards bill anything under a full inch as 4/4, so a board surfaced down to 13/16 inch still costs you the full 4/4 rate.

Quarter	Rough Thickness	Typical Surfaced (S2S)	Common Use
4/4	1 in	13/16 in	Drawer sides, panels, general work
5/4	1¼ in	1-1/16 in	Table tops, stair treads, shelving
6/4	1½ in	1-5/16 in	Chair parts, thicker tops
8/4	2 in	1¾ in	Legs, rails, heavier structural parts
12/4	3 in	2¾ in	Turnings, thick legs

The gap between the rough and surfaced columns is the part that costs money. You pay for the rough thickness and receive the surfaced one, so a 4/4 board billed at 1 inch arrives at roughly 13/16 after the mill takes both faces. If your design needs a finished ¾ inch, 4/4 works. If it needs a finished 1 inch, you must buy 5/4 and lose the difference.

Surfacing Codes

The abbreviation on the invoice tells you how much has already been removed:

• RGH: rough sawn, nothing surfaced. Full nominal thickness, but you do the milling.
• S2S: surfaced two sides. Faces planed, edges left rough. The most common way hardwood is sold.
• S3S: two faces and one edge, giving you a straight reference edge to rip from.
• S4S: all four sides. Ready to use, and priced accordingly.

Buying RGH gets you the most usable material per board foot if you have a planer and jointer. Without them, S2S or S4S is the practical choice, and the premium is really a machining fee.

Random Widths and the Real Waste Figure

Hardwood is generally sold random width and length rather than in dimensional sizes. You order a quantity of board feet and receive whatever boards make up that tally: a mix of widths, some with defects, some cupped or bowed.

This is why the 10% waste factor used for dimensional lumber is far too low for hardwood. Cutting around knots, checks, sapwood, and warp, then squaring rough edges, typically consumes 20–40% of the board footage depending on the grade and how demanding your cut list is. A project needing 40 finished board feet of clear stock should start from 50 to 55 board feet of FAS, and more if you are buying a lower grade.

Two practical consequences:

• Order the whole project at once. Colour and figure vary between trees and between lots, and a species like walnut or cherry can look noticeably different from a second purchase.
• Grade affects the waste factor more than the price difference suggests. A cheaper grade with more defects can cost more per usable board foot than FAS, once you account for what you cut away.

Board Feet, Linear Feet, and Square Feet

Three units, routinely confused, measuring three different things:

Unit	Measures	Used For
Board foot	Volume	Hardwood, rough lumber, anything priced by the mill tally
Linear foot	Length only	Trim, moulding, dimensional lumber sold by the piece
Square foot	Area	Sheet goods, flooring, decking coverage

The trap is quoting between them. A price “per foot” on trim means linear feet, and the width does not enter into it. A price “per foot” on hardwood almost certainly means board feet, and the width very much does. When comparing two quotes, confirm which foot each one means before assuming the cheaper number is cheaper. The construction unit conversions guide sets board feet alongside the other trade units, including roofing squares and bag counts.

Dimensional softwood is usually sold by the piece rather than by either measure (a 2×4×8 has a price, not a rate), which is why a framing order and a hardwood order need completely different arithmetic even when both are lumber.

That is also why a framing take-off counts pieces rather than volume: studs, plates, headers and blocking are each a count at a length. The framing calculator produces the order in those terms.