Board Foot Calculator
This calculator finds board feet from thickness, width, length, and quantity, using BF = (thickness" × width" × length") ÷ 144 × quantity — add a price per board foot for an instant material cost, and add as many rows as your cut list needs.
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Scenario presets
| Thickness (in) | Width (in) | Length | Qty | $/bf (optional) | Board feet | Actions |
|---|---|---|---|---|---|---|
| | 3.5 | |||||
| | 6.875 |
Enter actual milled dimensions (a 2x4 is actually 1.5" × 3.5") for a true board-foot count, or nominal dimensions if that is your supplier's convention — see the reference table below.
- Total cost
- —
How it works
A board foot is a volume: one square foot of lumber, one inch thick — 144 cubic inches. The formula just converts your board's three dimensions (in inches) into that unit, then multiplies by however many identical pieces you're buying.
BF = (thickness" × width" × length") ÷ 144 × quantity
- Thickness and width — enter in inches. Use actual (dressed) size for dimensional softwood, or the rough-sawn size your hardwood supplier bills against.
- Length — defaults to feet, matching how lumber is sold ("2x4x8" = 8 feet); switch to inches for a cut-list measurement.
- Quantity — the piece count for that row. Board footage scales linearly with it.
- Price per board foot — optional; leave blank to see quantities only.
Worked example
A deck project needs 12 joists, actual size 1½" × 7¼" (nominal 2x8), 12 feet long, at $1.85 per board foot.
Board feet per joist. (1.5 × 7.25 × 144) ÷ 144 = 1.5 × 7.25 = 10.875 BF (length in inches is 12 ft × 12 = 144", which cancels neatly against the 144 divisor at exactly 12 feet).
Total board feet. 10.875 × 12 = 130.5 BF.
Total cost. 130.5 × $1.85 = $241.43.
Nominal vs. actual lumber sizes
Dimensional softwood lumber is sold by nominal size but milled smaller. Sizes below follow the softwood lumber standard (NIST Voluntary Product Standard PS 20) that U.S. mills dress lumber to — use the actual column for a true board-foot count.
| Nominal | Actual (dressed) |
|---|---|
| 1x4 | ¾" × 3½" |
| 1x6 | ¾" × 5½" |
| 1x12 | ¾" × 11¼" |
| 2x4 | 1½" × 3½" |
| 2x6 | 1½" × 5½" |
| 2x8 | 1½" × 7¼" |
| 2x10 | 1½" × 9¼" |
| 2x12 | 1½" × 11¼" |
Tips from the field
- Confirm with your supplier whether they price by nominal or actual size before comparing quotes — the difference is meaningful on a large order.
- Add a separate row per distinct size rather than averaging dimensions across a mixed order.
- For hardwood bought by the board foot, use the rough-sawn thickness (4/4, 5/4, 8/4, etc.) the mill actually bills against.
- Round up piece counts before ordering — this calculator gives exact board footage, not a waste allowance.
What this tool does not do
- Does not size lumber for structural load — see the Joist Span Calculator for allowable spans.
- Does not account for cutting waste or kerf loss — add extra length or quantity if needed.
- Does not calculate rafter or framing geometry — see the Rafter Length Calculator.
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Frequently asked questions
These are the questions that come up at the lumber counter — nominal vs. actual size, how quantity multiplies, and what a board foot even is.
What exactly is a board foot?
A board foot is a volume measurement: one square foot of lumber, one inch thick. It equals 144 cubic inches. It is the standard unit for pricing hardwood and rough-sawn lumber, and is sometimes used for dimensional softwood too.
Should I use nominal or actual dimensions?
It depends on your supplier's convention. Hardwood and rough lumber is almost always priced by actual (rough-sawn) dimension. Dimensional softwood (2x4, 2x6, etc.) is dressed down from nominal size — a "2x4" is actually 1.5" × 3.5" — and some yards price by nominal size anyway. Ask, or check the invoice.
Why is a "2x4" not actually 2 inches by 4 inches?
Nominal size describes the rough, undressed lumber before it is planed (surfaced) smooth on all four sides. Planing removes about ½" from each nominal dimension, per the softwood lumber standard (NIST Voluntary Product Standard PS 20). A nominal 2x4 dresses down to an actual 1.5" × 3.5".
How does quantity affect the board foot total?
Board footage scales linearly with quantity — 10 identical boards have exactly 10× the board feet of one. Enter the piece count in the quantity field rather than adding 10 separate rows.
Can I mix different sizes in one calculation?
Yes — add a row for each distinct thickness/width/length combination and the calculator sums the total board feet (and cost, if priced) across all rows.
Is the length always entered in feet?
By default, yes, since that matches how lumber is sold ("2x4x8" means 8 feet long). Switch the row's unit selector to inches if you are working from a cut list measured in inches.
How do I calculate the cost of my lumber order?
Enter a price per board foot in the optional price field for each row — the calculator multiplies it by that row's board feet and adds every row's cost into the total.
Why do board feet matter for framing lumber, which is usually sold by the piece?
Framing lumber is priced by the piece or lineal foot at most yards, but board footage is still useful for comparing total material volume across a project, estimating waste, or pricing custom/rough-sawn lumber bought by the board foot.
What is the difference between a board foot and a linear foot?
A linear foot only measures length, ignoring width and thickness. A board foot accounts for all three dimensions, which is why a wide 2x12 racks up more board feet per linear foot than a narrow 2x4.
Does this calculator account for kerf loss from cutting?
No — it calculates the board footage of the material as specified. Add extra length or an extra row if you need to account for saw kerf or trimming waste.
What thickness should I use for rough-sawn hardwood measured in quarters (4/4, 8/4)?
4/4 means 1" thick rough-sawn (before drying and planing shrinkage), 8/4 means 2" thick, and so on. Enter the actual thickness you are being charged for — check with your supplier whether that is the rough or the surfaced dimension.
Why does my hand calculation come out slightly different?
Check that you and the calculator are using the same convention (nominal vs. actual) and the same length unit (feet vs. inches) — those two mismatches account for almost every discrepancy in board-foot math.
How we checked this page
- Written by
- Pitch & Span Editorial
- Reviewed by
- Formula checked against the standard board-foot definition (144 cubic inches per board foot); nominal-to-actual size table checked against NIST Voluntary Product Standard PS 20.
- Last reviewed
- 2026-07-28
- Publisher
- Pitch & Span
- Scope
- Lumber volume and cost estimating
- What we checked
-
- Worked example (12 joists, 1.5" × 7.25" × 12 ft, $1.85/bf) verified against the live calculator.
- Nominal-to-actual dimension table checked against standard softwood lumber dressing tolerances.
- Multi-row totals checked to sum correctly across mixed sizes and prices.
Cite this calculator
Pitch & Span. "Board Foot Calculator." Pitch & Span, https://pitchandspan.com/board-foot-calculator/. Accessed .
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