Deck Lumber Calculator
Calculate the decking boards, joists, and total board footage for any deck size. Enter your deck dimensions, board width, and joist spacing — the calculator gives you an accurate material list and cost estimate before you visit the lumber yard.
How to use this calculator
- Enter your deck length and width in feet.
- Choose your decking board width (5/4×6 is most common) and joist spacing (16" standard).
- Adjust the waste factor — 10% is standard for decks.
- Read your board count, joist count, total board feet, and cost estimate.
How we calculate this
Decking boards: total deck area ÷ coverage per board (actual board width in feet × board length), with a waste factor applied. Joists: (deck length ÷ joist spacing) + 1, rounded up, each joist running the full deck width. Board feet are calculated from nominal dimensions using (nominal thickness × nominal width × length) ÷ 12. A 10% waste factor is included by default to account for cuts at the perimeter and defects.
What this calculator doesn't include
This calculator estimates decking boards and joists only. It does not include beams, posts, ledger boards, rim joists, blocking, stair stringers, railings, or fasteners. Composite decking is not included — this calculator is designed for dimensional lumber. Pergolas, shade structures, or attached railings require separate calculations. Always verify structural member sizes with a structural engineer for elevated decks.
Example estimates — Deck Lumber
Pre-calculated for common project sizes. Includes 10% waste. Cost at ~$0.85/BF — adjust in the calculator above.
| Deck & Board Config | Boards | Joists | Total BF | With Waste | Est. Cost |
|---|---|---|---|---|---|
| 10×10 ft, 6" boards, 16" joists | 25 | 9 | 276.25 BF | 303.88 BF | $258.30 |
| 12×12 ft, 6" boards, 16" joists | 29 | 10 | 377.5 BF | 415.25 BF | $352.96 |
| 16×12 ft, 6" boards, 16" joists | 39 | 10 | 505.83 BF | 556.41 BF | $472.95 |
| 16×16 ft, 6" boards, 16" joists | 39 | 13 | 667.33 BF | 734.06 BF | $623.95 |
| 20×12 ft, 6" boards, 16" joists | 48 | 10 | 626.67 BF | 689.34 BF | $585.94 |
| 20×16 ft, 6" boards, 16" joists | 48 | 13 | 826.67 BF | 909.34 BF | $772.94 |
| 24×16 ft, 6" boards, 16" joists | 58 | 13 | 996 BF | 1095.6 BF | $931.26 |
| 10×10 ft, 4" boards, 16" joists | 38 | 9 | 278.33 BF | 306.16 BF | $260.24 |
| 16×12 ft, 4" boards, 16" joists | 59 | 10 | 508.33 BF | 559.16 BF | $475.29 |
| 20×16 ft, 4" boards, 16" joists | 74 | 13 | 840 BF | 924 BF | $785.40 |
Frequently asked questions
A 12×16 deck (192 sq ft) using 5/4×6 decking boards at 16" joist spacing requires approximately 40–44 decking boards (10% waste), plus 13 joists at 16 feet each. Total board footage runs roughly 350–400 BF depending on board length chosen. Use this calculator to get the exact count for your specific dimensions.
Pressure-treated Southern Yellow Pine is the most common and affordable choice for deck framing (joists, beams, posts). For the decking surface, options include pressure-treated pine, cedar, redwood, and Ipe (a Brazilian hardwood). Cedar and redwood resist rot and insects naturally and are easier to work with than Ipe, though Ipe lasts the longest. Composite decking is not lumber but is a popular alternative.
16" on-center is the most common joist spacing for residential decks and is required for 5/4 decking boards. 12" OC gives extra stiffness for 1" thick deck boards or for composite decking. 24" OC is sometimes used with thicker 2× decking in light-duty applications. Always check local building codes — many jurisdictions require permits and inspections for decks over 30" above grade.
5/4×6 (actual: 1" × 5.5") is the most popular deck board — it is lighter, easier to handle, and resists cupping better than 2×6. 2×6 is thicker and stiffer, making it a good choice for decks with 24" joist spacing or where extra strength is needed. 5/4×6 boards must be supported at 16" OC maximum.
A 1/8" to 1/4" gap between deck boards is standard. This gap allows water to drain and air to circulate, reducing rot and warping. If you are installing green (wet) pressure-treated lumber, boards can be butted tight — they will shrink to the right gap as they dry. Kiln-dried lumber should have the gap set at installation.