Worked example: boards for a 16 × 12 ft deck
Hypothetical educational example of a board takeoff. The 16 inch joist spacing is supplied by the scenario. It is not a span this site calculated. Footing diameter, soil and beam size are not in the result.
Inputs
| Board direction | 16 ft |
|---|---|
| Width | 12 ft |
| Actual board width | 5.5 in |
| Gap | 3/16 in |
| Stock | 16 ft |
| Joist spacing | 16 in, given |
| Waste | 10% |
| Screws per box | 350, a scenario default |
Arithmetic
- Rows = 144 ÷ 5.6875 = 25.32, which rounds up to 26.
- Linear length = 416 ft. With 10% that is 457.6 ft, or 28.6 boards of 16 ft, which rounds up to 29.
- Joists = 16 ft ÷ (16/12 ft) + 1 = 13.
- Screws = 26 × 13 × 2 = 676. Two boxes of 350 cover 700, leaving 24.
Required, waste and purchase
- Required
- 28.6 boards of 16 ft and 676 screws, using a spacing that was already chosen.
- Purchased
- 29 boards and 2 × 350-count boxes. Hidden clips, if used instead, are 338 and are not added on top of the screws. The 350 count is the calculator default, not a printed box we opened.
- Units
- US feet and inches. 5.5 in matches the actual width Trex lists for several of its boards. This example does not name a Trex line as the material being bought.
Assumptions
- Waste stays at this site’s 10% default. Trex’s article calls 5% a general rule of thumb. This example does not switch to 5%.
- No picture frame and no diagonal layout.
What this example does not decide
- Not a joist, beam, ledger or footing design. An allowable span comes from a code table or an engineer, including the American Wood Council span tools.
- No footing concrete is calculated here. If a plan already states tube diameter and depth, that volume is the sonotube calculator’s job.
Where to go next
- Deck board calculator — Run these inputs
- Deck board topic — Width, gap and the 10% versus 5% note
- How to plan a deck — Checklist around the takeoff
- Stain calculator — Finish after the boards are down
- Decking calculators — Tool list
Questions
Does 13 joists mean 16 inches on center is safe?
No. Thirteen is ceil(16 ft ÷ 16 in) + 1. The spacing was an input. Species, load and wet service are not inputs, and this page will not recommend them.
Why two screw boxes for 676 screws?
676 ÷ 350 is 1.93, so the purchase is 2 boxes (700 screws). The 24 extras are pack rounding. The 10% board waste is not applied to the screws.
Sources
- Trex – How many deck boards do I need? — accessed 2026-11-09: “The 1” Transcend® and Enhance® boards are .94” x 5.5”. The general rule of thumb is that you need 5% extra decking material to account for waste and mistakes.”