Introduction
Lumber buying has its own language — board feet, nominal sizes, grades, MBF — and most questions at the yard counter are the same dozen, asked in different words. This FAQ collects them in one place with straight answers: the units, the math, the pricing, and the buying decisions.
For any question with a number in it, the Lumber Cost Calculator does the arithmetic: enter nominal dimensions, quantity, price per board foot, and waste allowance for total board feet and total cost. The guides linked under each answer go deeper where it helps.
Units and the Board-Foot Formula
What is a board foot?
A unit of wood volume equal to a 12″ × 12″ × 1″ slab — 144 cubic inches, or about 0.0023597 m³. It’s the unit lumber is bought and sold by. Full derivation in the formula guide.
What is the board-foot formula?
(Nominal thickness in inches × nominal width in inches × length in feet) ÷ 12. A 2x6x12 is (2 × 6 × 12) ÷ 12 = 12 BF.
Do I use nominal or actual dimensions?
Always nominal — the size on the tag. A 2×6 is priced as 2″ × 6″ even though it actually measures 1.5″ × 5.5″. Using actual dimensions understates board footage by roughly 25–31%.
What are the actual dimensions of common lumber?
2×4 = 1.5″ × 3.5″; 2×6 = 1.5″ × 5.5″; 2×8 = 1.5″ × 7.25″; 2×10 = 1.5″ × 9.25″; 2×12 = 1.5″ × 11.25″; 4×4 = 3.5″ × 3.5″. One-by stock (1×6) surfaces to 0.75″ thick.
How many board feet are in a cubic meter?
About 423.78 BF per m³. To convert a per-m³ price to per-BF, divide by 423.78 — e.g., $530/m³ ≈ $1.25/BF.
Pricing
How much does a 2x6x12 cost?
It contains 12 board feet. At typical SPF #2 retail rates of $1.00–$1.50/BF, expect roughly $12–$18 per board before waste — the canonical example used across this whole article series.
What is a typical price per board foot for framing lumber?
SPF or southern yellow pine #2 typically retails around $0.90–$1.60/BF; Douglas fir runs $1.10–$1.80/BF. These are typical ranges with strong regional variation — verify locally. Full tiers in the cost guide.
Why do lumber prices change so often?
Lumber is a traded commodity: mill output, freight rates, tariffs, housing demand, and seasonality all move prices. Re-verify pricing within days of buying, and lock large orders with written quotes.
Is pressure-treated lumber more expensive?
Yes — typically 15–30% more than untreated kiln-dried lumber of the same size. It’s required by code for ground contact and exterior exposure; see the code compliance guide.
How much more does a higher grade cost?
Roughly: #1 runs 10–20% over #2, Select 30–60% over #2, and Utility/#3 about 20–30% under #2. But heavy culling of cheap grades can make #2 cheaper per usable board foot.
Buying and Estimating
How much waste should I add?
Ten percent is the standard starting point; 5–10% for clean straight runs, 12–15% for angles and short pieces, 15–20% for complex cuts or first-time DIY.
Is lumber cheaper at a lumberyard or a big-box store?
Close on small quantities; yards usually win 5–15% on volume, offer longer lengths and more species, and will pull and cull boards for you. The cost guide compares them line by line.
How do I compare a per-piece price to a per-BF quote?
Convert to per-BF: per-piece price ÷ BF per piece. A $15 tag on a 12-BF 2x6x12 equals $1.25/BF — directly comparable to a yard’s $1.25/BF quote.
What does MBF mean?
One thousand board feet. Yard quotes for large orders are often per MBF — $1,250/MBF is $1.25/BF.
How much lumber does a 12×24 ft deck need?
Roughly 1,500 board feet across decking, joists, beams, posts, and fascia — about $1,875 at a blended $1.25/BF, or ~$2,065 with 10% waste. The hypothetical deck case study (illustrative example) shows the full take-off.
What isn’t included in the calculator’s number?
Fasteners, hangers, concrete, delivery, and sales tax — typically another 15–30% on a deck project. Budget them as separate lines; the estimating guide shows how.
Codes and Materials
What lumber is required for ground contact?
Pressure-treated lumber rated UC4A or UC4B (ground-contact rated) — required by the IRC for posts, fence posts, and any wood touching soil. Standard “treated” without the right UC rating doesn’t qualify.
What fasteners work with pressure-treated lumber?
Hot-dip galvanized (ASTM A153) or stainless steel. Modern treatments (ACQ, MCA) corrode plain and electro-galvanized steel — inspectors check this.
What’s the difference between S4S and rough-sawn lumber?
S4S (surfaced four sides) is planed smooth on all faces and ready to use; rough-sawn is cheaper per BF but you’ll lose thickness planing it. Budget 20–30% waste on rough hardwood.
How should I store lumber before building?
Stacked flat on stickers (spacers) for airflow, off the ground, top covered. Wet-stacked or uncovered lumber warps — sometimes within days.
Should I let lumber acclimate before building?
For framing, a day or two stacked properly on site is plenty — kiln-dried framing lumber is already near indoor equilibrium moisture. For finish carpentry, hardwood flooring, or anything glued, give boards a week in the room they’ll live in. Big swings in moisture content are what cause gaps and warping later.
Related Guides
- Complete Guide — the full overview: calculator inputs, key terms, and the worked example.
- Board-Foot Formula Explained — the math behind every answer above.
- Lumber Cost Guide — species tiers, grade premiums, volatility, retail vs. yard.
- Species & Grade Guide — which wood for which job.
- Pro Tips — buying habits that cut 10–20% off the bill.
- Pre-Purchase Checklist — the final gate before money changes hands.
Get Your Number
Still have a question with a number in it? That’s what the Lumber Cost Calculator is for — plug in your dimensions, your local price per board foot, and your waste allowance, and get the answer in seconds.
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Actual lumber costs vary by species, grade, supplier, and market conditions. Verify prices with your local lumberyard and consult a licensed professional or your local building authority for structural or code-related decisions.
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