Board Foot Calculator

Lumber is sold by volume, not by the piece, which catches a lot of first-time woodworkers and contractors off guard at the lumber yard. Using a board foot calculator before you buy prevents costly over-ordering and eliminates embarrassing shortfalls mid-project. This guide explains the board foot unit from the ground up, walks through the formula, covers every common lumber size in a reference table, and answers the questions that most other resources skip entirely.

What Is a Board Foot?

A board foot is a unit of lumber volume equal to a piece that is 1 foot long, 1 foot wide, and 1 inch thick. In metric terms that works out to 144 cubic inches, or one-twelfth of a cubic foot. It is the standard buying and selling unit for hardwood lumber across the United States and Canada, and it is also used in the spray foam insulation industry, where a board foot describes how much volume one can of foam will fill.

The reason lumber is sold by board foot rather than by weight or piece count is that a single price per board foot stays consistent regardless of how the wood is dimensioned. A narrow, thick board and a wide, thin board of equal volume cost the same amount, which makes pricing transparent across dozens of species and sizes. The National Hardwood Lumber Association formally standardized this unit for hardwood trade in the United States, and their grading rules remain the industry reference today.

Board Foot Formula

The calculation is straightforward once you understand which dimensions go in which units. Length is always expressed in feet. Width and thickness are always expressed in inches.

Board Feet = Length (ft) x Width (in) x Thickness (in) / 12

If all three measurements happen to be in inches, divide by 144 instead of 12:

Board Feet = Length (in) x Width (in) x Thickness (in) / 144

The two formulas are mathematically identical since dividing by 12 after converting feet to inches is the same as dividing by 144. For a stack of multiple identical boards, multiply the result by the quantity.

How to Calculate Board Feet: Step-by-Step Example

Learning how to calculate board feet is easiest with a concrete example. Say you are buying five pieces of walnut for a dining table. Each board is 8 feet long, 10 inches wide, and 1.25 inches thick.

Step 1. Plug the single-board dimensions into the formula:

8 x 10 x 1.25 / 12 = 8.33 BF per board

Step 2. Multiply by the number of boards:

5 x 8.33 = 41.67 BF total

Step 3. If the supplier charges $4.15 per board foot, the total cost comes to:

41.67 x $4.15 = $172.92

The tool at the top of this page handles all three steps automatically and lets you switch between inches, feet, centimeters, and millimeters so you can calculate board feet from whatever measurements you have on hand.

Board Foot Reference Tables

Common Lumber Sizes: Board Feet per Linear Foot

This table lets you skip the calculation entirely for the most common dimensional sizes. Every figure uses nominal dimensions, which is how lumber is labeled at the yard.

Board Feet in a 2×4 at Common Lengths

Hardwood Lumber Thickness: The Quarter System

Softwood framing lumber is sold in familiar nominal sizes like 2×4 or 2×6. Hardwood lumber follows a different convention that confuses most beginners. Thickness is expressed in quarters of an inch, beginning at 4/4, which equals 1 inch, and stepping up in quarter-inch increments.

This system exists because hardwood is typically sold rough-sawn, and the quarter notation describes the rough thickness before any surfacing. When you surface a 4/4 board on both faces, the finished thickness drops to around 13/16 of an inch. Keeping rough and finished measurements separate prevents confusion when pricing.

Note: When entering thickness into the board feet calculator, use the nominal rough dimension unless you are pricing already-surfaced stock, in which case use the surfaced dimension.

How to Calculate Board Feet in a Log

A standard log board foot calculator uses one of two scaling methods: the Doyle Rule or the International 1/4-inch Rule. The Doyle Rule is the most widely used in the eastern United States for hardwood logs and uses this formula:

Board Feet = ((Diameter in inches - 4) / 4)^2 x Length in feet

Where diameter is measured at the small end of the log, inside the bark. So a log that is 16 inches in diameter and 12 feet long yields:

((16 - 4) / 4)^2 x 12 = 9^2 x 12 = 81 x 12 = 108 BF

The Doyle Rule tends to underestimate yield for small-diameter logs under 12 inches and overestimate it for very large logs. The International 1/4-inch Rule is more accurate across a wider range of diameters. The USDA Forest Products Laboratory publishes scaling tables for both methods if you need to work from reference charts rather than equations.

How Much Lumber Should You Buy? Planning for Waste

The raw board foot total from any calculation tells you the volume of finished lumber in your project. It does not account for what you lose on the way there. Buying exactly what the math says leaves you short almost every time.

Waste occurs at three points. First, rough lumber contains natural defects including knots, checks, and sapwood that you will cut away. Second, every saw cut wastes material in the kerf, which on a table saw or bandsaw is typically 1/8 of an inch per cut. Third, milling rough stock to flat, square dimensions removes material from every face.

As a practical rule, add 15 percent to your calculated total for clear softwood and furniture-grade hardwood. Add 20 to 25 percent for rough or lower-grade hardwood where defect removal is heavier. For live-edge slabs where you are keeping the natural edge and minimizing waste, 10 percent is usually enough.

Lumber to order = Calculated BF x 1.15 (furniture-grade hardwood)
Lumber to order = Calculated BF x 1.20 (rough or lower-grade hardwood)

Board Foot Price Guide

A board foot price calculator is only as useful as the price per board foot you feed into it. Prices shift with market conditions, region, and supplier, but the ranges below give you a reliable baseline for budgeting.

Common domestic softwoods such as pine, spruce, and Douglas fir typically run between $1.00 and $3.00 per board foot at retail. Domestic hardwoods such as red oak, poplar, and ash fall roughly between $3.00 and $6.00 per board foot depending on grade and thickness. Premium domestic hardwoods including walnut, hard maple, and cherry range from $6.00 to $12.00 or more at clear-select grade. Imported and exotic species vary widely but commonly start above $10.00 per board foot and climb much higher for rare figured pieces.

These are retail ballpark figures. Buying in volume from a hardwood dealer rather than a home center typically reduces the price by 20 to 40 percent. Always call your local supplier for current pricing before committing to a budget. Lumber prices have historically been volatile, with significant swings tied to housing demand and supply chain conditions.

Board Foot vs. Linear Foot vs. Square Foot

Three different units show up constantly when buying building materials, and mixing them up leads to expensive ordering errors. Here is how they relate:

The key distinction is that board footage and square footage are not interchangeable. If a supplier quotes flooring in square feet and you have measured your room in square feet, you are buying area coverage. If a hardwood dealer quotes you in board feet, you are buying volume, which means the thickness of the boards affects how much you need to order. A feet finder approach that carefully identifies which unit applies to each material before you buy prevents the single most common budgeting mistake in woodworking and construction.

Frequently Asked Questions (FAQ’s)