Lumber & Framing Calculator
Board feet, wall studs, joists and rafters, deck boards and fence materials — waste included, with the math shown and every dimension cited.
Your lumber take-off
Total board feet
5.33 bf
- Board feet per piece
- 5.33 bf
- Pieces
- 1
- Board feet use NOMINAL dimensions by convention: a 2×4 is figured as 2×4, though it actually measures 1.5×3.5.
How this is calculated
Board feet per piece
(thickness_in × width_in × length_ft) ÷ 12
= (2 × 4 × 8) ÷ 12
5.33 bf
Total board feet
board feet × quantity
= 5.33 × 1
5.33 bf
How to calculate board feet
Board feet is the volume unit lumber is priced in. The formula is (thickness in inches × width in inches × length in feet) ÷ 12 per piece. A 2×4 that is 8 ft long works out to (2 × 4 × 8) ÷ 12 = 5.33 board feet. Multiply by the number of pieces for the order total, then by your price per board foot for the cost. Board-foot math uses the nominal size by convention, even though a 2×4 really measures 1.5 by 3.5 inches.
Nominal vs actual lumber dimensions
| Nominal | Actual (inches) |
|---|---|
| 1× | 0.75 |
| 2× | 1.5 |
| 1× / 2× width 4 | 3.5 |
| width 6 | 5.5 |
| width 8 | 7.25 |
| width 10 | 9.25 |
| width 12 | 11.25 |
Studs by wall length (before corners and waste)
| Wall length | Studs at 16" OC | Studs at 24" OC |
|---|---|---|
| 8 ft | 7 | 5 |
| 10 ft | 9 | 6 |
| 12 ft | 10 | 7 |
| 16 ft | 13 | 9 |
| 20 ft | 16 | 11 |
| 24 ft | 19 | 13 |
Deck board coverage per row
| Board width | Gap | Coverage per row |
|---|---|---|
| 5.5 in | 1/8 in | 5.625 in |
| 5.5 in | 3/16 in | 5.6875 in |
| 5.5 in | 1/4 in | 5.75 in |
| 3.5 in | 1/8 in | 3.625 in |
Common lumber estimating mistakes
- •Mixing up nominal and actual sizes. Price board feet on the nominal size, but lay out framing on the actual size — a 2×4 is 1.5×3.5.
- •Forgetting the extra stud. A wall needs ceil(length ÷ spacing) plus one, then more for every corner and partition tie-in.
- •Ignoring the board gap on decks. A 1/8 inch gap across many rows adds up — count coverage as board width plus gap.
- •Using a layout count as a span rating. This tool counts pieces, not load capacity — size joists and rafters from your local code span tables.
- •Forgetting post footings. Deck piers and fence posts set in concrete — size each hole with the concrete calculator.
Frequently asked questions
How do you calculate board feet?+
Board feet = (thickness in inches × width in inches × length in feet) ÷ 12. A 2×4 that is 8 ft long is (2 × 4 × 8) ÷ 12 = 5.33 board feet. Multiply by the number of pieces for the total order.
Are board feet figured on nominal or actual size?+
Board-foot pricing conventionally uses the nominal size. A 2×4 is figured as 2 by 4 inches even though it actually measures 1.5 by 3.5 inches. Switch on the actual toggle only when you need the dressed volume.
How many studs do I need for a wall?+
Studs = ceil(wall length ÷ spacing) + 1. A 20 ft wall at 16 inches on center needs 16 field studs before adding two per corner, one per partition tie-in, and about 10% waste.
How many deck boards do I need?+
Rows = ceil(deck width in inches ÷ (board width + gap)). Multiply rows by the deck length for total linear feet, then divide by the board length and round up. A 5.5 inch board with a 1/8 inch gap covers 5.625 inches per row.
Lumber calculators by job
Board Feet
Figure board feet for pricing and ordering lumber. Enter thickness, width and length to get board feet per piece and the total — using nominal sizes by convention, with the math shown.
OpenStud / Wall
Count the studs and plate stock for a wall. Enter the wall length and spacing — add corners and partition tie-ins — to get the stud count and plate footage with waste included.
OpenDeck Boards
Count the deck boards for your project. Enter the deck size, board width and gap to get rows, linear feet and the number of boards by length — with waste included.
OpenFence
Count posts, rails and pickets for a fence. Enter the fence length, post spacing and picket width to get every material — and size the post footings with the concrete calculator.
OpenMethodology & sources
Counts use standard framing practice, carrying full precision and rounding up to whole pieces. Board feet use the conventional nominal size; switch to actual dressed dimensions for dressed volume. Stud, joist, deck and fence counts apply your waste factor and round up.
This tool counts pieces — it is not a structural span rating. Size joists, rafters and beams from the span tables in your local building code. Set deck piers and fence posts in concrete footings sized with the concrete calculator.
- American Softwood Lumber Standard PS 20-20 — nominal vs. actual dressed (S4S) sizes — verified June 28, 2026
Last reviewed June 28, 2026. Estimates are indicative — verify against current product specs and local requirements before ordering.
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