How many deck boards do I need for a 16 × 12 ft deck?
For the worked example (16 × 12 ft deck, 5½ in boards with ⅛ in gaps, 16 ft stock boards) the material list is Deck boards: 29 boards (calculated 26 rows × 1 board per row = 26 boards, based on 5.5 in boards, 0.125 in gaps, 16 ft stock, 10% extra). Quantities to buy are whole units rounded up from the calculated amounts. Enter your own measurements in the calculator above for your exact list.
How to use this calculator
- Enter the deck length (the way the boards run) and the width across the boards.
- Enter the actual width of your boards, the gap between them and the stock length you will buy. Read these from the product data.
- Keep or change the extra allowance, then read the rows, the boards per row and the number to buy.
- Copy, print or share the material list.
How this is calculated
- Rows = round up ((deck width + gap) ÷ (board width + gap))
- Rows cover rows × board width + (rows − 1) × gap, so no gap is charged after the last board
- Boards per row = round up (deck length ÷ stock length)
- Buy = round up (rows × boards per row × (1 + allowance ÷ 100))
Geometry is deterministic. Material coverage, density, installation waste and product yield can vary. We expose those assumptions so you can replace them with the values printed on the products you are actually buying. Treat every result as an estimate. Items on your list are labelled Calculated (straight from your measurements) or Estimated (depends on an assumption), and “Buy” quantities are whole units rounded up.
Sources
No third-party figure is built into this calculator. Quantities come from geometry and from the values you can see and edit under “Assumptions” below, each labelled by where it comes from.
Last reviewed: . See the methodology.
Assumptions
These starting values are used until you change them. They are typical, not universal. Check the label on the product you are buying.
| Assumption | Starting value | Where it comes from |
|---|---|---|
| Rows cover | n × board width + (n − 1) × gap | Mathematical – Gaps sit between boards, not after the last one |
| Actual board width | You enter it | You enter it (product / supplier) |
| Gap between boards | You enter it | You enter it (product / supplier) |
| Stock board length | You enter it | You enter it (product / supplier) |
| Extra allowance | 10% | Common planning default |
Worked example
A 16 × 12 ft deck with 5½ in boards, ⅛ in gaps, 16 ft stock boards and 10% extra:
- Deck boards: 29 boards (16 ft stock boards) · 5.5 in boards, 0.125 in gaps, 16 ft stock, 10% extra
Common questions
Which board width should I enter?
The actual width printed in the product data, not the nominal name. Nominal sizes are not the real width, and a small error in width changes the row count.
Is this a cut plan?
No. Each row is counted from whole stock boards. Butt joints, staggering and reusing offcuts can change the real number, so keep the extra allowance for your layout.
Does it include joists, posts or footings?
No. It estimates the surface boards only. The supporting structure is a design question for your plans, your local requirements and a qualified professional.