Introduction
A board foot is a standard unit of measurement used in the lumber industry. It equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long. Knowing how to calculate board feet is important when you are buying or selling lumber for a construction project. This Board Foot Calculator makes it quick and easy to figure out exactly how much lumber you need. Just enter the thickness, width, and length of your boards, along with the number of pieces, and the tool does the math for you. This helps you plan your materials, estimate costs, and avoid waste on your next building project.
How to use our Board Foot Calculator
Enter your lumber or log dimensions below, and this calculator will give you the total board feet and an optional cost estimate. The tool has two tabs: one for lumber boards and one for raw logs.
Lumber Board Feet Tab
Thickness — Type in the thickness of your board. You can use quarter notation like 4/4 or 8/4, a fraction like 1 1/2, or a decimal like 1.5. Then pick your unit (inches, feet, centimeters, or millimeters). The calculator will round your thickness up to the nearest quarter inch, which is how lumber is priced in the real world.
Width — Enter the width of your board as a whole number, fraction, or decimal. Choose your unit from the dropdown menu next to the field.
Length — Enter the length of your board. The default unit is feet, but you can switch to inches, centimeters, or millimeters if needed.
Quantity (Number of Boards) — Type in how many identical boards you have. The calculator will multiply the board feet per piece by this number to give you a total.
Price per Board Foot (optional) — If you want to know the total cost, enter the dollar amount you pay per board foot. Leave this blank if you only need the board footage.
Log Board Feet Tab
Small-End Diameter (inside bark) — Enter the diameter measured at the small end of the log, inside the bark. You can enter this in inches or centimeters.
Log Length — Enter the total length of the log in feet or meters. Common log lengths are 8, 10, 12, 14, and 16 feet.
Number of Logs — Enter how many identical logs you have. The calculator will show per-log results and totals for all logs when you have more than one.
Price per Board Foot (optional) — Enter a dollar amount per board foot to see cost estimates. The calculator shows results using three standard log scaling rules — Doyle, Scribner, and International ¼ inch — so you can compare board foot estimates and costs across each method.
What Is a Board Foot?
A board foot is the standard unit used to measure lumber volume in the United States and Canada. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long — or 144 cubic inches of wood. Lumber yards, sawmills, and hardwood dealers all use board feet to price and sell wood. If you want to know how much wood you need for a project or how much it will cost, you need to understand board feet.
How to Calculate Board Feet for Lumber
The board foot formula for sawn lumber is simple:
Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
For example, a board that is 1 inch thick, 6 inches wide, and 8 feet long equals 4 board feet. If you have 10 of those boards, you have 40 board feet total. The calculator above does this math for you instantly and also handles fractions, different units, and cost estimates.
What Is Quarter Thickness?
Hardwood lumber is often sold using a "quarter" system for thickness. In this system, 4/4 means the board is roughly 1 inch thick, 5/4 means about 1.25 inches, 6/4 means about 1.5 inches, and 8/4 means about 2 inches. Each "quarter" represents one-quarter of an inch. Lumber dealers round up to the nearest quarter when calculating board feet for pricing. This is called "quarterizing" the thickness, and the calculator above handles this automatically.
How to Calculate Board Feet from Logs
Estimating board feet from a raw log is different from measuring sawn lumber. Because a log is round and has bark, taper, and waste from sawing, you cannot get 100% of the wood turned into usable boards. Log scaling rules were created to estimate how many board feet of lumber a log will actually produce. Three main rules are used:
- Doyle Rule: This is the most common rule in the eastern United States, especially for hardwoods. It uses the formula BF = (D − 4)² × L ÷ 16, where D is the small-end diameter in inches and L is the length in feet. The Doyle rule tends to underestimate board feet for small logs and overestimate for large logs.
- Scribner Rule: This rule is widely used in the western United States for softwood species like pine and fir. It gives a more generous estimate than Doyle for smaller-diameter logs.
- International ¼-Inch Rule: This is considered the most accurate rule and is used by the USDA Forest Service. It accounts for a ¼-inch saw kerf and a taper of ½ inch every 4 feet. It almost always gives the highest estimate of the three rules.
The measurements you need for log scaling are the small-end diameter (measured inside the bark at the narrow end of the log) and the log length. Standard log lengths are typically 8, 10, 12, 14, or 16 feet.
Why Board Feet Matter in Construction and Woodworking
Board feet are the basis for buying and budgeting rough lumber. Whether you are framing a house, building furniture, or buying hardwood for flooring, knowing your board footage helps you order the right amount of material and avoid overspending. Prices for species like oak, walnut, cherry, and maple are almost always listed per board foot. By multiplying your total board feet by the price per board foot, you get your total lumber cost.
Board foot calculations also tie into other material estimates on a construction site. For instance, once you know your lumber needs, you may also need to figure out concrete for your foundation, drywall for interior walls, shingles for roofing, or insulation for energy efficiency. If you're building a deck, our decking calculator can help you estimate the material for the deck surface, while the board foot calculator covers your rough lumber needs. For projects that involve structural framing, our stud calculator and rafter calculator can help you determine the number of framing members required.
If you need to determine the total area of a room or project space before estimating lumber, try our square footage calculator. And for projects that combine lumber with masonry, tools like the brick calculator, mortar calculator, and concrete block calculator can round out your material planning.
Tips for Accurate Measurements
- Always measure the actual thickness of rough lumber, not the nominal size. A "1-inch" board from a sawmill is truly 1 inch thick before planing.
- For surfaced (S2S or S4S) lumber, you may still be charged based on the rough thickness before planing.
- When measuring width on boards with irregular edges (live edge or waney edge), use the average width.
- Add 10–20% extra to your total board footage to account for waste from cuts, defects, and unusable sections.