How to Calculate Board Feet of Lumber
I built this lumber calculator to help you figure out how many board feet you need and what the total cost will be before you head to the lumber yard. Board feet is the standard unit for buying hardwood and rough-sawn lumber, and it's calculated as: thickness (inches) × width (inches) × length (feet) ÷ 12. A 1" × 6" × 12' board contains 6 board feet; a 2" × 6" × 8' board contains 8 board feet.
Dimensional lumber (the framing studs and boards at home improvement stores) is sold by the linear foot rather than board feet, but the nominal dimensions are misleading. A "2 × 4" actually measures 1.5" × 3.5", and a "1 × 6" is actually 3/4" × 5.5". For rough lumber calculations, always use actual dimensions. For dimensional framing lumber, just multiply the number of pieces by the length you need.
Waste Allowances for Different Projects
No matter how carefully you plan, some lumber gets wasted. Here's a practical guide to waste percentages by project type:
- Basic framing (walls, floors, rafters): 10–15% waste for cuts and unusable ends.
- Cabinetry and furniture: 15–20% for defects, grain matching, and precision cuts.
- Exterior decking and siding: 10–15% for end trims and width adjustments.
- Hardwood projects with figured grain: 20–25% because you often reject boards with knots or defects in critical areas.
Choosing the Right Lumber Grade
Lumber grades tell you about the number and size of defects (knots, wane, splits) in a board. For structural framing, #2 grade is the standard — it has some knots but meets the load requirements for joists, studs, and beams. For finish work like trim, shelving, or furniture, you'll want Select or #1 grade to minimize knots and grain irregularities.
Hardwood grading follows a different system. FAS (Firsts and Seconds) is the top grade, suitable for fine furniture. No. 1 Common has more knots but is excellent for rustic furniture and flooring where character grain is desirable. Buying a lower grade and cutting around defects can save money on large projects — just add extra waste to your calculations.
Frequently Asked Questions
What is the difference between green and kiln-dried lumber?
Green (fresh-cut) lumber contains a high moisture content — often 30–100% by weight — and will shrink, warp, and check (develop surface cracks) as it dries. Kiln-dried lumber (KD or KD-HT) is dried to around 15–19% moisture content before sale and is much more dimensionally stable. For any interior finish work, furniture, or cabinet making, always use kiln-dried lumber. For exterior framing where the wood will be exposed to weather, pressure-treated is more important than kiln-dried.
How much does lumber cost per board foot?
Prices vary significantly by species, grade, and region. As a rough benchmark, dimensional pine framing lumber runs $0.50–$1.50 per board foot. Common hardwoods like poplar and maple range from $3–$6 per board foot. Walnut, cherry, and oak run $5–$12 per board foot. Exotic species like teak, padauk, or purpleheart can exceed $20 per board foot. Check with your local lumber yard or hardwood dealer for current pricing — lumber prices fluctuate significantly with housing markets.
Should I buy lumber at a big-box store or a lumber yard?
For framing lumber, big-box stores (Home Depot, Lowe's) are convenient and competitively priced. For finish work, hardwoods, or unusual dimensions, a dedicated lumber yard is usually better — higher grade selection, knowledgeable staff, and the ability to hand-pick boards. Many lumber yards also offer milling services (planing, jointing, ripping to width) that big-box stores don't, which saves significant time on furniture and cabinet projects.