What Is a Board Foot?
A board foot is a unit of lumber volume equal to a piece of wood that is 1 inch thick, 12 inches wide, and 1 foot long - or any combination of dimensions that equals the same volume. It is the standard unit used by sawmills and hardwood dealers to price and sell lumber in North America.
If you have ever bought dimensional lumber at a big-box store (2x4s, 2x6s), you may have paid by the linear foot or by the piece. But when buying hardwood from a lumber yard, or estimating material for a larger project, board feet is the unit you need to know.
The Board Foot Formula
The formula uses thickness and width in inches, and length in feet:
Where thickness and width are in inches, and length is in feet. If your length is in inches, divide by 144 instead of 12:
For a faster calculation, use our board feet calculator - enter your dimensions and it totals everything up instantly.
Nominal vs. Actual Dimensions
This is the part that trips up most beginners. Lumber at the store is labeled by its nominal size, but the piece you actually receive is smaller. The wood is cut to the nominal size when green, then dried and surfaced, which reduces its dimensions.
Common examples:
- A 1x4 is actually 0.75" thick × 3.5" wide
- A 1x6 is actually 0.75" thick × 5.5" wide
- A 1x8 is actually 0.75" thick × 7.25" wide
- A 2x4 is actually 1.5" thick × 3.5" wide
- A 2x6 is actually 1.5" thick × 5.5" wide
- A 2x8 is actually 1.5" thick × 7.25" wide
When calculating board feet for pricing purposes at a hardwood dealer, use the nominal dimensions - that is how lumber yards calculate their price. When calculating how much wood you actually have for your project (cut lists, joinery), use the actual dimensions.
Worked Example: Building a Set of Shelves
Say you are building a simple bookshelf with three shelves, each made from a 1x10 board cut to 48 inches (4 feet) long.
Each shelf:
Three shelves total: 3.33 × 3 = 10 board feet
Add a 15% waste factor for cuts and defects: 10 × 1.15 = 11.5 board feet
You would order 12 board feet to be safe, which might be two 8-foot 1x10 boards (each gives you about 6.67 board feet).
How to Calculate Board Feet for a Full Project
For any project with multiple pieces, calculate each component separately and add them together:
- Write out a cut list of every piece of wood in your project (thickness, width, length).
- Calculate the board feet for each piece using the formula above.
- Add all the board foot values together for your raw total.
- Multiply by 1.10 to 1.15 to add a waste and defect buffer (10 to 15%).
- Round up to the nearest board or standard length available at your supplier.
Buying slightly more than you calculated is always better than running short mid-project. Lumber lots can vary in color and grain, so boards from a second purchase may not match your first batch.
Board Feet vs. Linear Feet
Linear feet measures only length - it does not account for thickness or width. Stores that sell pre-cut dimensional lumber (2x4s, 2x6s) often price by the linear foot because the width and thickness are fixed and standardized. Board feet is a volume measurement and accounts for all three dimensions, which is why it is used when comparing pieces of different sizes or buying rough-cut hardwood where dimensions vary.
If a lumber yard quotes you a price per board foot and you have a cut list, you can calculate your total cost by multiplying your total board feet by the price per board foot.
Frequently Asked Questions
Do I use nominal or actual dimensions in the formula?
It depends on the context. For pricing at a lumber yard, use nominal dimensions - that is how they measure. For project planning (figuring out if a piece will actually fit), use actual dimensions. The difference matters most with 2x lumber, where a 2x4 is actually 1.5" x 3.5", not 2" x 4".
How much extra lumber should I buy?
Add 10% for clean, straight lumber from a reliable supplier. Add 15% if you are buying rough-cut hardwood (which may have more defects, wane, or checking), working with a complex cut list with many small pieces, or if you are new to the project type and expect some mistakes. For painted projects where grain matching is not a concern, 10% is usually enough.
How do I calculate board feet for lumber sold by the piece?
If a store sells lumber by the piece (a single 8-foot 2x4 for a set price), you may not need to calculate board feet at all for purchasing. But it is still useful to know the board footage of each piece so you can compare prices between suppliers who charge by different units. Divide the total price by the board footage to get the price per board foot for a true apples-to-apples comparison.
What is a board foot of hardwood worth?
Hardwood prices vary widely by species, grade, and region. Common hardwoods like poplar or soft maple typically run $3 to $6 per board foot. Mid-range species like cherry or walnut are commonly $8 to $15 per board foot. Exotic or figured wood can run $20 to $50 or more. Prices at retail lumber yards are significantly higher than buying direct from a sawmill.
Can I calculate board feet for plywood or sheet goods?
Technically yes, but board feet is rarely used for plywood. Sheet goods are almost always sold by the sheet (typically 4x8 feet) or by the square foot. Board feet is primarily a hardwood and rough lumber measurement. If you need to calculate coverage for a plywood project, calculate the square footage of your surfaces instead and divide by 32 (the square footage of a standard 4x8 sheet).