How to use
- Put the dimension parallel to the boards in the length field. Width runs across the rows.
- Enter actual board width, side gap, available stock length, and your planned joist spacing.
- Review the row and linear-length totals before using the rounded board count as a shopping allowance.
How the estimate is calculated
Rows = deck width in inches ÷ (board width + gap), rounded up. Linear feet = rows × deck length. Purchased boards = linear feet × (1 + allowance ÷ 100) ÷ stock length, rounded up. Joist lines = deck length in inches ÷ spacing, rounded up, plus an end line. The face-fastener example uses two fasteners at each row and joist intersection.
Example: for 16 × 12 ft, 5.5 in boards, a 3/16 in gap, 16 ft stock, 16 in joist spacing, and 10% extra: 144 ÷ 5.6875 rounds up to 26 rows. That is 416 linear ft and 29 boards after the allowance. There are 13 joist lines, giving 26 × 13 × 2 = 676 fasteners.
What the defaults mean
| Input | Initial value | How to use it |
|---|---|---|
| Board width | 5.5 in | Example actual width; measure your decking |
| Side gap | 3/16 in | Commonly used planning figure |
| Support spacing | 16 in on center | Commonly used planning figure |
| Face fasteners | 2 per intersection | Planning assumption for this takeoff |
| Stock allowance | 10% | Editable allowance for cuts |
The Trex span-chart search summary and Advantage Lumber guidance are the background for these gap, spacing, and fastening assumptions; the original charts were not available for review. They are not installation requirements. Follow your decking maker's span and gap chart, including its rules for angled boards or hidden clips.
A board count is not a cutting plan
The stock estimate pools all linear length. If a row is longer than your stock, its joints need suitable support, and leftovers may not fit another row. Picture-frame borders, stairs, fascia, blocking, beams, posts, and footings are excluded. Plan those separately. Framing and footing design should follow local requirements and the applicable AWC DCA 6 guidance; this tool does not check either.
Common mistakes
- Swapping along-board length and across-board width after selecting a board direction.
- Treating the support-line count as a complete structural lumber list.
- Buying hidden clips from the two-face-fastener estimate without checking the clip system.
- Assuming linear footage guarantees that stock lengths can make every cut.
Sources
Planning context: Trex span-chart summary and Advantage Lumber gap and fastening guidance reviewed only as search-summary information. No span limit is represented as code. Conversions use NIST's exact inch-to-millimeter relationship.
Related calculators
- Board Foot Calculator — lumber volume for a separate material list
- Stair Calculator — explore stair dimensions for a separate layout
Frequently asked questions
Does this design a safe deck frame?
No. It counts surface boards and support lines using your spacing. Beam spans, connections, loads, and footings require separate design.
Which direction is deck length?
Length follows the boards. Width crosses the board rows. Changing that direction can change both row count and cutting waste.
Are hidden fasteners included?
The estimate assumes two face fasteners per row at each joist line. Hidden clips have a different product-specific count.
Why might I need more than the board result?
The calculation pools linear footage. Unsupported seams, unusable offcuts, borders, and special layouts can require additional stock.
Can I use the default gap for any board?
Check the product instructions first. Material, moisture, temperature, and fastening system can change the required gap.