Published August 15, 2026 · Updated August 23, 2026 · By Tupep
What this is and what it is not
This is a materials takeoff method. It turns a deck’s dimensions and a joist spacing into a list of boards, hangers and fasteners you can hand to a lumber yard. It is not a design. Joist size, beam size, post size, footing size and depth, and ledger attachment all have to come from your local code’s prescriptive deck tables or from a licensed designer, and be reviewed by your building department. Those numbers depend on species, grade, spacing, span, snow load and soil, and none of that belongs in a calculator. We get the sizes first, then count them.
The counting formula
- Joists = (length along the house in inches / spacing) rounded down, then + 1
- Ledger = 1 board the full length along the house
- Rim / outer band = 1 board the full length along the house
- End joists = the first and last joist in the count above, no extras needed
- Beam = plies x beam length, plies from your code table
- Blocking = (joists minus 1) pieces per row, each cut to the clear bay width
Worked example: 10 ft out from the house, 12 ft along it, 16 in on center
The 12 ft dimension runs along the house, so joists are spaced across it. 12 ft is 144 in. 144 / 16 = 9 spaces, and 9 + 1 = 10 joists, with the first and last acting as the outside end joists. Each joist is 10 ft long.
Ledger is one 12 ft board. Rim is one 12 ft board. The beam, however many plies your code table calls for, is 12 ft per ply; assume two plies here, so two 12 ft boards. One row of mid-span blocking uses 9 pieces cut to the clear bay width, which for 16 in on center with 1.5 in joists is 14.5 in. Nine pieces at 14.5 in is 130.5 in, so a single 12 ft board yields all of them with room to spare.
| Member | Pieces | Length each | Lineal ft |
|---|---|---|---|
| Joists | 10 | 10 ft | 100 |
| Ledger | 1 | 12 ft | 12 |
| Rim / outer band | 1 | 12 ft | 12 |
| Beam plies | 2 | 12 ft | 24 |
| Blocking, one row | 9 cut from 1 board | 14.5 in each | 12 |
| Total framing stock | 10 at 10 ft, 5 at 12 ft | 160 |
Check the arithmetic: ten boards at 10 ft is 100 ft, five boards at 12 ft is 60 ft, total 160 lineal feet. All of it has to be lumber rated for exterior use and ground contact where required, and the ledger and anything within reach of splash gets the same treatment.
Hardware, which is half the job
Framing hardware is where deck lists go wrong, because the count is not obvious and the wrong part is a safety problem rather than an inconvenience.
| Item | Count | Notes |
|---|---|---|
| Joist hangers at the ledger | 8 | Interior joists only; the two end joists are usually attached differently |
| Joist hangers at the beam or rim | 0 or 8 | Zero if joists bear on top of the beam, 8 if they hang |
| Hanger nails or hanger screws | Per hanger manufacturer | Every hole filled with the specified fastener |
| Post bases | Per code table post count | Standoff type keeps end grain off concrete |
| Post caps | Same as post count | Positive connection beam to post |
| Ledger fasteners | Per code and manufacturer schedule | Spacing and edge distance are code items |
| Beam ply fasteners | Per manufacturer | Built-up beams have a nailing or bolting pattern |
| Ledger flashing | 13 lineal ft | Continuous, lapped correctly with the house weather barrier |
The two details that separate a good frame from a callback
Use the fastener the hanger is rated for, in every hole. A joist hanger is tested as a system with a specific nail or structural screw. Ordinary deck screws are not that fastener and are brittle in shear. A hanger with three of its ten holes filled with deck screws is not a rated connection, it is decoration. The same goes for finish: pressure treated lumber uses copper based preservatives that corrode ordinary galvanized steel, so hardware and fasteners have to match the treatment chemistry.
Crown every joist and install crown up. Sight down each board and mark the high side of the curve. Crown up, the load flattens the joist over time. Crown down, you have permanently built a dip into the deck surface that no decking will hide.
Setting the ledger height
The ledger elevation determines the finished deck height, and the number you want is not the door threshold. Work down from it: the top of the decking should sit below the door sill by enough that water and snow do not sit against the door, commonly a couple of inches. Then ledger top = desired top of decking minus decking thickness. With 5/4 decking at 1 in of actual thickness, the ledger top is 1 in below the finished walking surface. Get that wrong and you either build a step at the doorway or you build a water problem.
Flashing over the ledger is a code item in most places. We install the ledger, flash it, then hang joists, because sliding flashing behind a framed deck is a bad afternoon.
Decking on top, briefly
The 10 ft depth is 120 in. With 5/4×6 decking at 5.5 in of face, 21 rows gives 115.5 in of wood, leaving 4.5 in across 20 gaps, or 0.225 in each. Twenty one rows of 12 ft boards is 252 lineal feet before waste, a separate order that changes none of the numbers above.
One more time, because it matters: this list counts pieces. The size of those pieces, the footing design and the connection to the house must come from your local code tables or a designer, and be approved by your building department. Frost depth for the footings is jurisdiction dependent and varies widely, so confirm it locally before anybody digs.
Related guides
- Composite vs Wood: Board Length and Waste
- How Many Deck Boards for a 12×16 Deck
- Picture Frame Border: Extra Boards and Blocking
- Gate Framing: What the Calculator Does Not Count
Sources and Further Reading
Run your own numbers with the Deck Board Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
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