Board Foot Calculator

If you’ve ever tried to compare lumber sizes and pricing across boards, slabs, or beams, you’ve probably bumped into board feet. A board foot is a volume unit used in woodworking and lumber sales, and it makes mixed dimensions easier to compare on a single scale.

This board foot calculator converts your thickness, width, and length into board feet per piece, multiplies by quantity, and optionally adds a waste factor for offcuts and defects. If you enter a price per board foot, you’ll also get a quick cost estimate.

For more tools like this, browse All Calculators or explore the Engineering Calculators category for measurement and planning helpers.

Calculator

Engineering Calculators

Thickness required

Tip: 1 inch = 25.4 mm.

Width required

Remember: nominal sizes can differ from actual planed width.

Length required

Board-foot math uses length in feet internally.

Quantity 1–9999

pieces

If you’re planning a project list, consider saving your totals from All Calculators for quick comparisons.

Waste factor (optional) 0–50%

Waste covers kerf, trimming, checks, knots, and “oops” cuts. For rough layout work, 8–15% is common.

Price per board foot (optional) ≥ 0

per BF

Leave blank if you only want volume. If your yard prices by the BF, this gives a fast estimate.

Display precision 0–4 decimals

display

We round shown numbers to your selection while keeping internal calculations at higher precision.

Enter values like 1,250 if you want—commas are handled safely.

Total board feet (with waste)

Based on your dimensions, quantity, and waste %.

0BF

Base total Total with waste

Calculation Summary

Per piece: 0 BF

Base total: 0 BF

Waste: 0% → Total with waste: 0 BF

Step-by-step breakdown

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Want to compare volume formats? You can pair this with measurement tools in Engineering Calculators for planning and conversion checks.

What your result means

Lumber is often priced and compared using board feet because it standardizes thickness, width, and length into one volume number. Use Total with waste when you’re buying material, and use Base total when you’re estimating “ideal” volume before offcuts.

How it works

Board foot definition: 1 board foot is the volume of a board that is 1 inch thick × 12 inches wide × 12 inches long.

This calculator converts your inputs into standard units, then applies the classic board-foot formula:


Convert to standard units:
• T_in = thickness in inches
• W_in = width in inches
• L_ft = length in feet

Board feet per piece:
BoardFeet_per_piece = (T_in × W_in × L_ft) / 12

Totals:
TotalBoardFeet = BoardFeet_per_piece × Quantity

Waste:
WasteMultiplier = 1 + (WastePercent / 100)
TotalWithWaste = TotalBoardFeet × WasteMultiplier

Cost (optional):
EstimatedCost = TotalWithWaste × PricePerBoardFoot

Variable definitions

T_in: thickness after converting inches or millimeters to inches.
W_in: width after converting inches or millimeters to inches.
L_ft: length after converting feet, meters, or inches to feet.
Quantity: number of identical pieces you’re calculating.
WastePercent: extra percentage for kerf/offcuts/defects (0–50%).
PricePerBoardFoot: optional price to estimate total cost.

Why divide by 12? Because a board foot is based on 12 inches of width in a one-foot length. Multiplying inches × inches × feet gives “inch-inch-foot,” and dividing by 12 converts that to board feet.

Use cases

Buying rough lumber for furniture builds: Estimate how many board feet you need for a table top, legs, and aprons, then add a waste factor for milling and joinery.
Comparing yard prices across thicknesses: Convert 4/4 and 8/4 boards into board feet so you can compare cost fairly even when the dimensions differ.
Planning beams or large timbers: Use the calculator for thick stock (like 3" or 4" beams) where small rounding errors can add up fast in totals.
Project takeoffs for shelving or cabinetry: Multiply per-piece board feet by quantity to get a clean purchasing number for repeated parts.
Pricing custom slabs: If a supplier sells by the BF, plug in slab dimensions and price per BF to estimate your material cost before you commit.

Examples

Example 1 (common board): Thickness 1.5 in, width 5.5 in, length 8 ft, quantity 12, waste 10%.
Per piece = (1.5 × 5.5 × 8) / 12 = 5.5 BF. Base total = 5.5 × 12 = 66 BF. With waste = 66 × 1.10 = 72.6 BF.
Example 2 (metric thickness/width): Thickness 38 mm, width 140 mm, length 2.4 m, quantity 6, waste 8%.
Convert: T_in = 38/25.4 = 1.4961 in, W_in = 140/25.4 = 5.5118 in, L_ft = 2.4×3.28084 = 7.8740 ft.
Per piece = (1.4961 × 5.5118 × 7.8740) / 12 ≈ 5.401 BF. Base total ≈ 32.406 BF. With waste ≈ 32.406 × 1.08 ≈ 34.998 BF.
Example 3 (big beam): Thickness 4 in, width 6 in, length 12 ft, quantity 3, waste 12%.
Per piece = (4 × 6 × 12) / 12 = 24 BF. Base total = 24 × 3 = 72 BF. With waste = 72 × 1.12 = 80.64 BF.

Common Mistakes

Mixing inches and feet without converting: Board-foot math assumes thickness/width in inches and length in feet. A unit mismatch can throw results off by 12× or more.
Using nominal sizes as actual: A “2×6” isn’t usually 2"×6" after milling. Use the actual measured thickness/width if you want accurate volume.
Forgetting quantity: Per-piece board feet can look reasonable, but the purchase number is almost always the multiplied total.
Setting waste to 0% on cut-heavy projects: Sheet-goods style planning doesn’t translate perfectly to lumber. Kerf and trimming are real, especially with rough stock.
Treating price as mandatory: Price per BF is optional—leave it blank if you’re only computing volume.

Quick Tips

Measure after milling if you’re checking yield: If your goal is “how much did I actually end up with,” use final planed dimensions.
Add 8–15% waste for general furniture work: More if you’re matching grain or color, less if parts are forgiving and stock is clean.
Round up when buying: Suppliers stock in real boards, not perfect decimals. Use the “with waste” total as your purchase target.
Watch length units: If you input inches for length, make sure the unit selector is set to inches so it converts to feet correctly.
Keep precision practical: Two decimals is usually plenty. Higher precision helps when you’re summing many items or comparing close quotes.

FAQ

What is a board foot, and why is it used for lumber?

A board foot is a volume unit equal to a board that is 1 inch thick, 12 inches wide, and 12 inches long. Lumber comes in many thicknesses and widths, so board feet give buyers and sellers a consistent way to compare volume across different sizes. If two boards have the same board-foot total, they contain the same amount of wood volume even if one is thicker and the other is wider. That’s why many hardwood yards price stock “per BF.”

Do I enter thickness and width in inches even if my tape is metric?

You can enter thickness and width in either inches or millimeters—just choose the correct unit next to each input. The calculator converts millimeters to inches internally (25.4 mm per inch) because board-foot formulas are traditionally defined using inches for thickness and width. This lets you work in whatever system you measured in while still getting a standard board-foot answer. If your measurements include decimals or commas (like 1,250), the calculator will interpret them safely.

Why is length handled in feet instead of inches?

Board-foot calculations commonly use thickness and width in inches and length in feet because a board foot is based on a one-foot length (12 inches). Using feet keeps the formula clean: (T_in × W_in × L_ft) ÷ 12. If you measured length in meters or inches, the calculator converts it to feet first. This approach also matches how lumber is often sold—lengths are typically quoted in feet, even when other dimensions are in inches.

What does the waste factor change in the result?

Waste factor increases your base board-foot total to account for real-world loss: saw kerf, trimming, checking, knots, tear-out, and layout inefficiencies. The calculator multiplies your base total by (1 + waste%/100). For example, 10% waste turns 66 BF into 72.6 BF. Use the “Total with waste” number when planning a purchase so you’re less likely to come up short. If your project requires color matching or grain selection, you may want a higher waste percentage.

How accurate is the result if I use nominal lumber sizes?

Accuracy depends on whether the dimensions you enter match the wood you’re actually buying or using. Nominal sizes (like 2×6) are often smaller in real, planed dimensions, so using nominal numbers can overstate board feet. If you want the most accurate volume and cost estimate, measure actual thickness and width with a ruler or calipers and enter those values. If you’re only doing a quick comparison and your supplier prices by nominal categories, using nominal numbers can still be useful—just be consistent.

Can I estimate cost reliably with price per board foot?

Yes, as long as the price you enter matches how your supplier bills. Many hardwood suppliers price rough lumber per board foot, so multiplying “Total with waste” by price per BF gives a practical estimate. Keep in mind that extras like milling fees, minimum purchase quantities, taxes, or special figure premiums are not included here. If your supplier prices by the piece or by linear foot, you may need a different method. When in doubt, use this cost as a planning baseline and verify with the yard’s quote.

Why do my results look slightly different from a supplier’s tally?

Small differences usually come from rounding practices, measurement conventions, or how the supplier treats irregular boards. This calculator lets you pick display precision, but internal calculations keep higher precision to reduce rounding drift. A supplier may round each board’s BF up to the nearest tenth or quarter, or measure width at the narrowest point of a board. Some places also bill “tally” board feet based on their own measurement standards. If you need to match a yard’s method, try aligning your precision and rounding choices with their billing policy.

What’s the best way to measure boards for this calculator?

Measure thickness and width across the usable portion of the board, then measure length along the board’s long edge. For rough lumber, thickness can vary, so take a couple readings and use a realistic average if you’re estimating a batch. If boards are irregular, you can approximate width using an average of the wide and narrow ends, or break the board into sections and compute totals separately. For accurate buying, use the measurement approach your supplier uses so your numbers align with the invoice.

Sources & References

Board foot standard definition: 1 in × 12 in × 12 in volume basis used in lumber measurement.
Unit conversions: inch–millimeter conversion (25.4 mm per inch) and meter–foot conversion (1 m = 3.28084 ft).
Common trade practice: Lumber volume comparison and pricing often uses board feet for hardwoods and rough stock.

Trust & Accuracy

Accuracy note: Calculations run locally in your browser. No server processing is used for this tool.

Rounding & precision: Display values are rounded to your chosen precision (0–4 decimals). Internally, calculations keep higher precision to reduce rounding drift across steps.

Privacy-first: No input data is transmitted or stored. Everything stays on your device.