Estimating a 16 x 12 ft Deck, Frame to Boards
The deck calculator’s 16 × 12 worked example, extended downward through the framing it rests on — beam, posts and footings — so the whole structure is on one shopping list.
Calculators used
The project
A 16 × 12 ft deck attached to the house on a ledger: joists span the 12 ft direction from ledger to a beam along the 16 ft edge, decking runs the 16 ft direction. Loads flow boards → joists → beam → posts → footings, and the takeoff below follows the same path top-down — each layer sized by the one above it.
Decking: 29 boards and 9 lb of screws
Straight from the deck calculator’s worked example: 5/4 x 6 boards (5.5 in face) with a 1/4 in gap across 12 ft needs 26 rows; at 16 ft a row and 10% waste, that is 29 boards of 16 ft. Two screws at every board-joist crossing makes 676 screws ≈ 9 lb at 75 per pound. Dry boards get the 1/4 in gap; wet pressure-treated boards are laid nearly tight and shrink their own gap.
Joists: 13 × 2x8 at 16 in centres
Joists at 16 in on centre along the 16 ft edge: floor(16 ÷ 1.333) + 1 = 13 joists, each spanning the 12 ft to the beam — within the typical span of a treated 2x8 at this spacing, with a joist hanger at every ledger connection. Add two 16 ft 2x8s for the rim and blocking stock, and flash the ledger properly: ledger failure is the classic deck collapse, and it is a flashing detail, not a lumber quantity.
Beam and posts: (2) 2x10 on three 6x6s
A doubled 2x10 under 12 ft joists is good for roughly 6.5 ft between posts — the conservative table in the post-spacing guide — so the 16 ft beam takes three 6x6 posts: two ends and one centre. That is two 16 ft 2x10s, three posts, three post bases and connection hardware. Verify the exact span against the code beam table for your lumber before digging.
Footings: 13 bags of concrete
Three footings, 12 in diameter, 36 in deep (below frost where required — same logic as a fence post, carrying far more load):
π × 0.5² × 3 ft = 2.36 cu ft each; ×3 = 7.1 cu ft; +10% = 7.8 cu ft → 13 bags of 80 lb mix — comfortably bag territory, mixed one footing at a time. The concrete calculator’s column mode does this per hole.
The shopping list
| Layer | Item | Quantity |
|---|---|---|
| Decking | 5/4x6 boards, 16 ft | 29 |
| Decking | Deck screws, 2-1/2 in | 9 lb |
| Frame | 2x8 joists, 12 ft | 13 |
| Frame | 2x8 rim/blocking, 16 ft | 2 |
| Frame | Joist hangers + ledger flashing | 13 + 16 lf |
| Beam | 2x10, 16 ft | 2 |
| Posts | 6x6 with base + cap hardware | 3 |
| Footings | 80 lb concrete + cardboard tube forms | 13 bags + 3 tubes |
If the deck is more than a step off grade
Add the stair package: the stair calculator sizes risers and treads from your exact drop, and a 36 in wide flight with wood treads takes three 2x12 stringers. Guardrails become mandatory at heights set by local code — commonly 30 in.
Frequently asked questions
How many footings does a 16x12 deck need?
Three, under the beam along the 16 ft edge, when the other side hangs on a house ledger. A freestanding version replaces the ledger with a second beam and three more footings.
What size beam does a 16x12 deck need?
A doubled 2x10 with posts about every 6.5 feet is the typical answer for 12 ft joists, or a doubled 2x12 to stretch toward 8 ft spacing. The binding numbers are in the IRC beam table for your species and joist span.
Can I build a 16x12 deck without a permit?
Usually not — most US jurisdictions permit and inspect decks above a minimal size or height, and attached decks almost always qualify. The inspection mostly checks footings, the ledger and guards, which are exactly the failure points worth a second pair of eyes.