Board Foot Calculator Guide: How to Buy Rough Lumber by the Board Foot

What Is a Board Foot?

A board foot is a unit of volume equal to a piece of wood 1 inch thick, 12 inches wide, and 12 inches long (144 cubic inches). It's the standard unit for pricing and selling hardwood lumber in North America. One board foot = 1" × 12" × 12" = 144 cubic inches.

The board foot system exists because hardwood lumber comes in random widths and random lengths. A typical hardwood board might be 6 inches wide and 9 feet long, while the next board from the same stack might be 11 inches wide and 7 feet long. You can't price by the linear foot when every board is a different size. Pricing by the board foot normalizes the volume so that a wide board costs proportionally more than a narrow board of the same length and thickness.

When you buy 100 board feet of 4/4 walnut, you might get fifteen boards that are each different widths and lengths, but their total volume equals 100 board feet. The dealer pulls boards from the stack, measures each one, tallies the board feet, and invoices the total.

Board feet are always calculated based on the nominal (rough) thickness, not the surfaced thickness. A 4/4 board (nominally 1 inch thick) that has been planed to 13/16" is still calculated as 1 inch thick for board foot purposes. You're buying the volume of wood the sawmill produced, not the volume after planing.

The Board Foot Formula

Board Feet = (Thickness in inches × Width in inches × Length in inches) ÷ 144. Or equivalently: Board Feet = (Thickness" × Width" × Length in feet) ÷ 12. Both formulas give the same result; use whichever is more convenient.

Example 1: A board that is 1" thick, 8" wide, and 10 feet long. BF = (1 × 8 × 10) ÷ 12 = 6.67 board feet.

Example 2: A board that is 2" thick (8/4), 6" wide, and 8 feet long. BF = (2 × 6 × 8) ÷ 12 = 8.0 board feet.

Example 3: A board that is 1.5" thick (6/4), 10" wide, and 12 feet long. BF = (1.5 × 10 × 12) ÷ 12 = 15.0 board feet.

For boards with fractional widths (which is almost always the case with random-width lumber), the dealer typically rounds width to the nearest inch or half-inch. A board that's 7-1/4" wide might be tallied as 7" or 7.5" depending on the dealer's rounding convention. Most dealers round down, which works in your favor.

Some dealers use a "board foot tally stick" or "lumber rule" — a calibrated measuring stick that directly reads board feet for a given width and length at standard thicknesses. You lay the stick across the board's width, read the board feet off the scale, done. These are becoming less common as dealers switch to electronic tally systems, but you'll still see them at smaller operations.

The Quarter-Thickness System: 4/4 Through 16/4

Hardwood lumber thickness is specified in quarters of an inch. This system dates back centuries and is universal in the North American hardwood industry. The notation is read as "four-quarter," "five-quarter," etc.

4/4 (four-quarter): 1 inch thick (rough). After surfacing (planing both faces), yields approximately 13/16" or 3/4" usable thickness. This is the most common thickness for furniture, cabinets, and general woodworking.

5/4 (five-quarter): 1-1/4" thick (rough). After surfacing, yields approximately 1-1/16" or 1". Used when you need a full 1" finished thickness, which 4/4 can't provide after surfacing. Also used for thicker shelves, tabletop edges, and trim.

6/4 (six-quarter): 1-1/2" thick (rough). Yields approximately 1-5/16" after surfacing. Used for thicker table legs, rails, and structural furniture components.

8/4 (eight-quarter): 2" thick (rough). Yields approximately 1-3/4" after surfacing. Used for heavy table legs, workbench tops, turnings, and laminated panels where thickness matters.

10/4, 12/4, 16/4: 2-1/2", 3", and 4" thick respectively. These are specialty thicknesses used for turning blanks, carving blocks, timber-frame joinery, and thick slabs. They're significantly more expensive per board foot than 4/4 because they come from larger logs and require longer drying times. Not all species are readily available in thick stock.

The important thing to understand is that the quarter designation is the ROUGH thickness. The actual thickness of rough-sawn lumber may vary by 1/16" to 1/8" from nominal depending on the sawmill. A 4/4 board might actually measure anywhere from 15/16" to 1-1/16". This is normal and expected. The surfacing process removes the variation and produces a consistent finished thickness.

Rough vs. S2S vs. SLR: Surfacing Options

Rough (RGH): Lumber as it comes off the saw. Both faces show saw marks, the edges are waney (bark edge) or rough-sawn, and the thickness varies slightly. Rough lumber is the cheapest per board foot and gives you maximum thickness to work with. It requires a jointer and planer (or a CNC surfacing operation) to produce flat, parallel faces. Most serious woodworkers and production shops buy rough because it gives them control over the final thickness and flatness.

S2S (Surfaced Two Sides): The dealer runs the lumber through a planer to produce flat, parallel faces at a specified thickness. The edges are still rough or waney. S2S lumber costs more per board foot (typically $0.15-$0.40/BF surcharge) but saves you the surfacing step. It's a good option if you don't have a planer or if you're buying a small quantity where setting up the planer isn't worth the time.

SLR (Straight Line Rip): One edge of the board is ripped straight on a rip saw, giving you one straight reference edge. SLR is useful if you don't have a jointer to straighten edges. Some dealers offer S2S1E (surfaced two sides, one edge) which combines planing and one straight edge.

S4S (Surfaced Four Sides): Both faces planed and both edges jointed/ripped. This is essentially ready-to-use lumber. It's the most expensive option and is less common at hardwood dealers because most of their customers prefer to do their own surfacing for maximum control. When available, S4S comes at a significant premium.

The decision between rough and surfaced depends on your equipment and volume. If you have a jointer and planer, buying rough saves money and lets you mill to your exact desired thickness. If you're a hobbyist without surfacing equipment, S2S is worth the surcharge. For CNC production where the router will surface the workpiece anyway, rough lumber is the obvious choice.

Species Pricing: What to Expect

Hardwood lumber prices vary enormously by species. Understanding the price tiers helps you budget projects and choose species that fit both your aesthetic and your wallet. Prices fluctuate with market conditions, but the relative positioning of species is fairly stable.

Budget tier ($3-$6/BF for 4/4 FAS): Poplar (the cheapest domestic hardwood, great for painted work), soft maple (lighter and cheaper than hard maple), red oak (abundant and affordable), ash (strong and flexible, good for tool handles).

Mid-range ($6-$10/BF for 4/4 FAS): Hard maple (the standard for cutting boards and workbenches), white oak (excellent for outdoor furniture, boat building, and whiskey barrels), hickory (extremely hard and shock-resistant), birch (consistent grain, good for plywood-matching solid edging).

Premium ($10-$18/BF for 4/4 FAS): Black walnut (the darling of American furniture making — prices have risen significantly), cherry (beautiful color that deepens with age and UV exposure), quartersawn white oak (ray fleck figure commands a premium over flat-sawn).

Exotic/specialty ($15-$40+/BF): Mahogany (genuine Swietenia, not African "mahogany"), teak (naturally oily, weather-resistant), purpleheart, padauk, wenge, and other tropical species. Figured domestic woods (curly maple, bird's eye maple, figured walnut) also fall in this range. Prices for figured wood vary wildly based on the quality and intensity of the figure.

Thickness affects price per board foot. Thicker stock costs more per BF because it comes from larger logs, takes longer to dry, and has higher waste in processing. As a rough guide: 5/4 is 10-15% more than 4/4, 8/4 is 25-40% more than 4/4, and 12/4 and above can be 50-100% more than 4/4 for the same species and grade.

Waste Factors: How Much Extra to Buy

You will never use 100% of the lumber you buy. Defects, saw kerf, surfacing loss, end checks, and project errors all consume material. The waste factor you apply depends on the lumber grade, the complexity of the project, and your skill level.

FAS grade lumber (highest grade): FAS (First and Seconds) boards are at least 83.3% clear (free of defects). Expect 15-25% waste for a typical furniture project. This includes surfacing loss (~3/16" per board), end trimming (check ends where drying cracks extend into the board), and crosscut waste from working around the 16.7% maximum defect allowance.

#1 Common grade: At least 66.7% clear. Expect 25-40% waste. You'll spend more time working around knots, mineral streaks, and other defects. #1 Common is significantly cheaper than FAS (typically 30-50% less per BF) and is a good value if your project uses shorter parts that can be cut between defects.

#2 Common grade: At least 50% clear. Expect 40-55% waste. This grade is appropriate for rustic furniture, small parts, and projects that incorporate the character marks as design features. At half the price of FAS (or less), it can be economical even with high waste if you have a use for the clear sections.

Project-specific waste: Beyond grade-related waste, add 5-10% for saw kerf (each rip cut wastes 1/8" of material), 5% for jointing edges (removing 1/16" to 1/8" per edge), and 5-10% for mistakes and test cuts. A conservative total waste factor for a furniture project in FAS lumber is 30%. For #1 Common, use 40-50%.

The practical calculation: if your project needs 40 board feet of finished parts, buy 40 × 1.30 = 52 board feet of FAS lumber, or 40 × 1.45 = 58 board feet of #1 Common. The extra cost of buying 30-45% more lumber is offset by avoiding the dreaded situation of being one board short at the end of a project and having to make a separate trip to the dealer (and hope they still have matching material from the same lot).

Buying Tips and Nominal vs. Actual Sizes

Visit the dealer in person. Buying hardwood lumber sight-unseen (online or by phone) means you get whatever the dealer pulls from the stack. Visiting in person lets you hand-select boards for color consistency, grain pattern, and figure. Most hardwood dealers allow customers to sort through the stack. This is standard practice, not a special request.

Bring a moisture meter. Properly kiln-dried hardwood should be 6-8% moisture content. Green or air-dried lumber (15-25% MC) will continue to shrink and warp as it dries in your shop. If the dealer says "kiln dried" but your meter reads 12%, the lumber was kiln dried but has re-absorbed moisture in storage. It's still usable but should be acclimated in your shop for 1-2 weeks before milling.

Understand random widths and lengths. Hardwood lumber comes in random widths (typically 4" to 12"+ for domestic species) and random lengths (typically 6 to 16 feet). You cannot order all 8" wide boards. If you need consistent widths, buy wider boards and rip them to your width. If you need short pieces, buy long boards and crosscut them. Buying long, wide boards maximizes your yield from each piece.

Nominal vs. actual for softwood construction lumber: Unlike hardwood, construction lumber (dimensional lumber) at the big box store is sold by nominal size. A 2x4 is actually 1.5" × 3.5". A 1x6 is actually 3/4" × 5.5". A 2x12 is actually 1.5" × 11.25". These nominal-to-actual conversions are defined by the American Lumber Standards Committee. Hardwood lumber doesn't have this discrepancy — a 4/4 rough board is actually ~1" thick.

Ask about quantity discounts. Many hardwood dealers offer per-board-foot discounts on orders over 100 BF, 250 BF, or 500 BF. If your project needs 80 BF, it might be cheaper to buy 100 BF at the discounted price (and keep the extra as shop stock) than to buy exactly 80 BF at the standard price.

Buy from the same lot for color consistency. Boards from the same tree or the same drying batch tend to have more consistent color and grain. If color matching is important (table tops, cabinet doors), ask the dealer if the stack is from a single lot. Buying all your project wood at once from one stack ensures consistency that's impossible to replicate on a second trip.