Reference chart
Deck Board Chart & Calculator
Deck boards, screws and joists for the common deck sizes at 5½-inch boards with a ⅛-inch gap, 16-foot stock and 5% waste. The calculator below takes any size, board width, gap and stock length.
Boards needed by deck size
| Deck (W × L ft) | Sq ft | Boards across | Boards to buy16 ft, +5% | Linear ft | Screws | Joists @16″ |
|---|---|---|---|---|---|---|
| 8 × 10 | 80 | 18 | 19 | 304 | 280 | 9 |
| 10 × 10 | 100 | 22 | 24 | 384 | 350 | 9 |
| 10 × 12 | 120 | 22 | 24 | 384 | 420 | 10 |
| 12 × 12 | 144 | 26 | 28 | 448 | 504 | 10 |
| 12 × 16 | 192 | 26 | 28 | 448 | 672 | 13 |
| 14 × 16 | 224 | 30 | 32 | 512 | 784 | 13 |
| 16 × 16 | 256 | 35 | 37 | 592 | 896 | 13 |
| 16 × 20 | 320 | 35 | 74 | 1184 | 1120 | 16 |
| 20 × 20 | 400 | 43 | 91 | 1456 | 1400 | 16 |
| 16 × 24 | 384 | 35 | 74 | 1184 | 1344 | 19 |
| 20 × 24 | 480 | 43 | 91 | 1456 | 1680 | 19 |
| 24 × 24 | 576 | 52 | 110 | 1760 | 2016 | 19 |
Your numbers
Boards to buy
28
26 across × 1 per row, +5%
Linear feet
448
192 sq ft of deck
Screws
672
2 per board per joist at 16″
Joists at 16″
13
across the length
across = ceil((width×12 + gap) ÷ (board + gap)) = 26; rows along the length = ceil(16 ÷ 16) = 1. Stagger joints on a joist; buy stock that lets you skip joints entirely if the deck is 16 or 20 ft long.
Questions
How many deck boards do I need?
Divide the deck width (across the boards) by the board width plus the gap, round up, then multiply by the number of boards needed along the length at your stock length, and add 5% for waste. A 12 × 16 deck with 5½-inch boards and a ⅛-inch gap needs 26 boards across; at 16-foot stock that is one per row, so 26, plus waste is 28.
How much gap between deck boards?
⅛ inch for kiln-dried lumber and composite, per most manufacturers; up to ¼ inch in wet climates. Wet pressure-treated boards are laid tight because they shrink to a gap as they dry. The chart uses ⅛ inch.
How many screws per deck board?
Two at every joist. At 16-inch joist spacing that is about 350 screws per 100 square feet, which the chart rounds to 3.5 per square foot. Hidden fasteners for grooved composite are one clip per board per joist.
How many joists?
Deck length in inches ÷ 16 + 1 at 16-inch centres, running perpendicular to the boards. Composite decking often requires 12-inch centres for diagonal runs or some brands; check the span chart on the decking, and use the IRC R507 joist span table for the joist size.
Should I run boards the long way?
Boards run perpendicular to the joists, so the joist direction decides it. Running boards along the longer dimension with stock that spans it end to end avoids butt joints, which is why the calculator asks for stock length: a 16-foot deck with 16-foot boards has no joints at all.
Charts are computed from the formulas and code figures stated on the page (International Residential Code limits where cited). They are planning and take-off numbers, not engineering: species, grade, span tables and local amendments govern anything structural. Confirm with your inspector before you cut.