Deck Board Calculator
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.
Your lumber take-off
Deck boards (waste included)
30 boards
- Rows
- 35 rows
- Total linear feet
- 420 ft
How this is calculated
Rows of decking
ceil(deck_width_in ÷ (board_width_in + gap_in))
= ceil(192 ÷ (5.5 + 0.125))
35 rows
Linear feet
rows × deck_length
= 35 × 12
420 ft
Boards (with waste)
ceil(ceil(linear_ft ÷ board_length) × (1 + waste% ÷ 100))
= ceil(27 × (1 + 10 ÷ 100))
30 boards
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 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.
What gap should I leave between deck boards?+
A 1/8 inch gap is typical for dry pressure-treated and composite boards to allow drainage and expansion. Wet lumber can be butted tighter because it shrinks as it dries.
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.
Methodology & sources
Counts follow standard framing practice with full precision, rounding up to whole pieces and applying your waste factor. Board feet use the conventional nominal size. This tool counts pieces — it is not a structural span rating; size members from your local code span tables.
- 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.
We're committed to keeping these tools accurate and improving them over time. If you'd like to contribute to their accuracy, or you run into any issues or errors, please email us at info@tradesppl.com.