Decking
29 boards
Deck boards
Use the board count as a starting point, then confirm the exact board size and length, and add extra for diagonal or picture-frame layouts.
Deck calculator
Deck calculator for deck boards and joists.
Enter deck size, board size, and joist spacing to estimate deck boards and joists. A 16 x 12 ft deck needs about 29 boards and 13 joists.
16 x 12 deck
29 boards
13 joists
Decking
461 ft
linear feet with waste
Joist spacing
16 in
on center, typical
Quick reference
Deck boards and joists for common deck sizes
5.5 in wide boards in 16 ft lengths with the default 10% waste, and joists at 16 in on center.
| Deck size | Area | 16 ft boards | Decking linear feet | Joists |
|---|---|---|---|---|
| 10 x 10 ft | 100 sq ft | 15 | 240 ft | 9 |
| 12 x 12 ft | 144 sq ft | 22 | 346 ft | 10 |
| 12 x 16 ft | 192 sq ft | 29 | 461 ft | 13 |
| 16 x 20 ft | 320 sq ft | 48 | 768 ft | 16 |
| 20 x 20 ft | 400 sq ft | 60 | 960 ft | 16 |
Deck boards run across the joists. Joist count comes from the deck length; joist length is the deck width.
Quick deck answers
Common deck sizes
12 x 12 deck
144 sq ft
22 boards
about 10 joists
16 x 12 deck
192 sq ft
29 boards
about 13 joists
20 x 16 deck
320 sq ft
48 boards
about 16 joists
Posts need footings
Deck posts sit on concrete footings. Estimate the concrete per footing with the post-hole calculator using your footing diameter and depth.
Shopping list
Decking, framing, and fasteners
Board and joist counts update from the calculator. Confirm board size, framing spans, and fastener type before ordering.
Framing
13 joists
Joists, beams, and ledger
The joist count assumes a simple rectangular frame. Beams, posts, ledger board, and rim joists are sized from your deck plan and span.
Fasteners
Screws, hangers, and hidden clips
Plan deck screws or hidden fasteners, joist hangers, and structural connectors. Hidden-clip systems are priced per square foot.
Footings
Concrete footings
Deck posts sit on concrete footings. Estimate the concrete per footing with the post-hole calculator using your hole size and depth.
Formula shown
How the deck estimate works
1. Deck area and board coverage
area = length x width; board = (width in / 12) x length ft
2. Board count
boards = ceil(area x (1 + waste) / board coverage)
3. Joists
joists = ceil(length x 12 / joist spacing) + 1
Framing is more than joists
The joist count is for a simple rectangular field. Beams, posts, ledger board, rim joists, blocking, stairs, and railings come from your deck plan and span tables, and structural members must meet local code.
Sources
- Decks.com board and framing layout — deck board coverage and joist spacing norms
- Lumber dimensions reference — nominal vs actual decking board widths
Sources checked
Checked against
Deck and fence layout rules and installed-cost ranges checked against published building and cost guides.
How we check our numbersLast updated: June 25, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
FAQ
Deck calculator questions
Deck boards, joists, waste, and concrete footings for deck posts.
How many deck boards do I need? + -
Divide the deck area (plus waste) by the coverage of one board. A 16 x 12 ft deck (192 sq ft) with 5.5 in by 16 ft boards and 10% waste needs about 29 boards. Wider or longer boards reduce the count.
How many joists do I need for a deck? + -
Joists are usually 16 inches on center. A 16 ft long deck frame needs about 13 joists at 16 in spacing, plus beams, ledger, and rim joists from your plan. Closer spacing (12 in) adds joists and stiffness.
How much waste should I add for deck boards? + -
About 10% covers straight-layout cuts on a simple rectangle. Diagonal decking, picture-frame borders, and angled or multi-level decks use more, so bump the waste up for those.
Do deck posts need concrete? + -
Yes, deck posts sit on concrete footings. The amount depends on the footing diameter and depth, not the deck area. Estimate it with the post-hole concrete calculator using your footing size.