Every deck calculator will tell you how many decking boards to buy. The question people actually search is bigger: what is the whole lumber list for a 12x16, a 14x28, a 6x20? The answer depends mostly on one number most lists ignore — how far the deck projects from the house — because that decides the joist size, and the joist size decides everything underneath.
The tables below are worked out in advance for twelve common sizes using the same logic as the deck lumber calculator. Sizes are written length along the house x projection out from the house. A "12x16" in a plan can mean either; check which way yours runs before reading a row, because it changes the answer.
Assumptions Behind Every Row
- Attached to the house with a ledger, one beam line at the outer edge, no cantilever.
- No. 2 Southern pine framing, joists at 16 in on center, sized from IRC 2021 Table R507.6.
- Beam: 2-ply 2x10, post spacing from the beam span for the load it carries.
- 6x6 posts; footings 12 in diameter by 36 in deep; 80 lb concrete bags.
- 5.5 in decking with a 3/16 in gap, running parallel to the house, in the board length that wastes least, plus 5%.
Change any of those — a freestanding deck, a different species, 12 in spacing, a deeper frost line — and the numbers move. The calculator handles all of them.
Framing: Joists, Posts and Footings
| Deck (along x out) | Joist size | Joists | Posts | Concrete bags |
|---|---|---|---|---|
| 8 x 8 | 2x6 | 7 @ 8 ft | 2 | 8 |
| 10 x 10 | 2x8 | 8 @ 10 ft | 3 | 12 |
| 12 x 10 | 2x8 | 10 @ 10 ft | 3 | 12 |
| 12 x 12 | 2x10 | 10 @ 12 ft | 3 | 12 |
| 16 x 12 | 2x10 | 13 @ 12 ft | 3 | 12 |
| 16 x 14 | 2x10 | 13 @ 14 ft | 4 | 16 |
| 20 x 6 | 2x6 | 16 @ 8 ft | 4 | 16 |
| 20 x 12 | 2x10 | 16 @ 12 ft | 4 | 16 |
| 20 x 14 | 2x10 | 16 @ 14 ft | 4 | 16 |
| 20 x 16 | 2x12 | 16 @ 16 ft | 4 | 16 |
| 24 x 12 | 2x10 | 19 @ 12 ft | 4 | 16 |
| 28 x 14 | 2x10 | 22 @ 14 ft | 5 | 20 |
Every row also needs a rim board and a ledger along the house side at the same depth as the joists (never smaller than 2x8 for the ledger), and two 2x10s per 16 ft of beam. On decks longer than 16 ft, the rim, ledger and beam boards are spliced, with beam splices landing over a post.
Decking and Hardware
| Deck (along x out) | Decking boards | Deck screws | Joist hangers | Hurricane ties |
|---|---|---|---|---|
| 8 x 8 | 18 @ 12 ft | 238 | 7 | 7 |
| 10 x 10 | 24 @ 12 ft | 352 | 8 | 8 |
| 12 x 10 | 24 @ 12 ft | 440 | 10 | 10 |
| 12 x 12 | 28 @ 12 ft | 520 | 10 | 10 |
| 16 x 12 | 28 @ 16 ft | 676 | 13 | 13 |
| 16 x 14 | 32 @ 16 ft | 780 | 13 | 13 |
| 20 x 6 | 14 @ 20 ft | 416 | 16 | 16 |
| 20 x 12 | 28 @ 20 ft | 832 | 16 | 16 |
| 20 x 14 | 32 @ 20 ft | 960 | 16 | 16 |
| 20 x 16 | 36 @ 20 ft | 1,088 | 16 | 16 |
| 24 x 12 | 55 @ 12 ft | 988 | 19 | 19 |
| 28 x 14 | 63 @ 16 ft | 1,320 | 22 | 22 |
Screws are two per board at every joist. If you are using composite decking with hidden fasteners, count clips instead: roughly one per board per joist.
The Projection Breakpoints
Read down the joist column and a pattern appears. The length along the house barely matters to the joist size; the projection decides it, in steps. At 16 in on center in Southern pine:
| Projection up to | Joist |
|---|---|
| 9 ft 0 in | 2x6 |
| 11 ft 10 in | 2x8 |
| 14 ft 0 in | 2x10 |
| 16 ft 6 in | 2x12 |
| Beyond 16 ft 6 in | Intermediate beam or 12 in spacing |
Two consequences are worth planning around. First, the extremely common 12 ft projection sits just past the 2x8 limit, so a 12 ft deck needs 2x10 joists even though 2x8 looks close enough on paper. Second, the jump from 14 to 15 ft out moves you from 2x10 to 2x12 and adds a post, which is why a deck sketched at 15 ft is often cheaper redrawn at 14.
Same Area, Different Bill: 16x12 vs. 12x16
Both are 192 square feet. Built 16 ft along the house and 12 ft out, the joists are thirteen 2x10s at 12 ft — about 260 board feet of joist lumber. Turn it 90 degrees to 12 ft along and 16 ft out, and the span forces ten 2x12s at 16 ft — about 320 board feet, roughly 23% more framing, and each piece is heavier and harder to source straight.
If the space allows either orientation, running the long dimension along the house is almost always the cheaper deck to frame.
What Changes the List
- Freestanding. Without a ledger you need a second beam line, which doubles the posts and footings. The 16x12 above goes from 3 posts and 12 bags of concrete to 6 posts and 24 bags.
- Douglas fir, hem-fir or SPF. These span less than Southern pine. The same 16x12 steps up to 2x12 joists and 4 posts.
- Very deep decks. Past 16 ft 6 in out, no joist size clears the span at 16 in on center. A 20x20 deck adds a mid beam and drops back to 2x8 joists, but ends up with 10 posts instead of 4. Tightening to 12 in spacing with 2x12s is often the cheaper route.
- Composite decking. Many composites require 12 in joist spacing, which adds joists but also lengthens the allowable span. Check the decking manufacturer before you pick the frame.
- Height and guards. Decks more than 30 in above grade need guards, and guard posts need blocking the take-off above does not include.
Before You Order
These are planning take-offs from the prescriptive tables, not a stamped design. Footing size, ledger fastening and guard attachment are set by your local code, and most attached decks need a permit. Take the list to the permit counter first; it is much cheaper to change a sketch than a frame.
Frequently Asked Questions
How much lumber do I need for a 12x16 deck?
Built 16 ft along the house and 12 ft out with a ledger at 16 in on center in Southern pine: 13 2x10 joists at 12 ft, a 16 ft rim and ledger, two 2x10s for the beam, 3 posts, 12 bags of concrete, 28 decking boards at 16 ft and about 676 screws. Built the other way, 12 ft along and 16 ft out, it needs ten 2x12 joists at 16 ft instead.
What lumber do I need for a 14x28 deck?
For 28 ft along the house and 14 ft out: 22 2x10 joists at 14 ft, rim and ledger of two 16 ft pieces each, four 2x10s for the beam, 5 posts, 20 bags of concrete, 63 decking boards at 16 ft and about 1,320 screws. At 14 ft the 2x10s are right at their maximum span, so many builders use 2x12 or 12 in spacing for a stiffer floor.
How much lumber for a 6x20 deck?
A deck 20 ft along the house and 6 ft out only needs 2x6 joists, since 2x6 spans 9 ft at 16 in on center. That is 16 joists at 8 ft, rim and ledger of two 16 ft pieces each (the ledger at 2x8 minimum), four 2x10 beam boards, 4 posts, 16 bags of concrete, 14 decking boards at 20 ft and about 416 screws.
Why does a 12 ft deck need 2x10 joists instead of 2x8?
Because a No. 2 Southern pine 2x8 at 16 in on center has a maximum span of 11 ft 10 in, just short of 12 ft. The span is measured from the face of the ledger to the face of the beam, so a 12 ft projection with the beam at the outer edge exceeds it. Either step up to 2x10, tighten the spacing to 12 in, or set the beam in and cantilever the last foot.
Does the deck length along the house change the joist size?
No. The length along the house changes how many joists you need, the beam length and the post count. Only the projection, meaning the distance the joists span from the ledger to the beam, decides the joist size. That is why turning the same deck 90 degrees can change the framing bill by a quarter.