Calculators / Deck
Deck Calculator
A 12 × 16 ft deck with pressure-treated boards needs 29 deck boards 16 ft long (458 linear ft with 10% extra), 13 joists 12 ft long at 16 in spacing, about 710 deck screws and 4 footings. Enter your deck below.
Count your deck materials
| Deck area | 192 sq ft |
|---|---|
| Board rows across the width | 26 |
| Decking, linear feet with extra | 458 ft |
| Joist length | 12 ft |
| Deck screws | 710 |
| Hidden fasteners (composite) | Not needed |
| Railing posts (6 ft apart or less) | 6 |
| Balusters, 2 × 2 (gap under 4 in) | 65, gap 3.45 in |
| Top and bottom rails | 60 ft |
How much will it cost? Building a 12 × 16 ft raised wood deck with railing and stairs typically costs $15,340 with a contractor. Deck building cost in your state
How we count deck materials
- Boards: rows = width (in) ÷ (5.5 in board + gap), rounded up. Linear feet = rows × length × (1 + extra); boards = linear feet ÷ board length, rounded up.
- Joists: length (in) ÷ spacing, rounded up, plus one. Each joist spans the deck width.
- Screws: two at every place a board crosses a joist, as the building code requires for wood decking, plus 5%.
- Footings: about one per 60 sq ft, at least two; a freestanding deck needs a second row instead of the house ledger.
The code limits come from the International Residential Code, section R507. Snow load, frost depth and local amendments change footing and beam sizes, so check your local code before you build.
Materials for common deck sizes
Pressure-treated wood, 16 ft boards, 16 in joist spacing, 10% extra, attached to the house.
| Deck | Boards | Joists | Screws | Footings |
|---|---|---|---|---|
| 10 × 10 ft | 16 | 9 | 416 | 2 |
| 12 × 12 ft | 22 | 10 | 546 | 3 |
| 16 × 12 ft | 29 | 10 | 735 | 4 |
| 16 × 16 ft | 39 | 13 | 956 | 5 |
| 20 × 16 ft | 48 | 13 | 1,174 | 6 |
| 20 × 20 ft | 60 | 16 | 1,445 | 7 |
| 24 × 16 ft | 58 | 13 | 1,420 | 7 |
Common questions
How many deck boards do I need for a 12 × 16 deck?
With 5.5 in boards running along the 16 ft side, you need 26 rows: 29 boards 16 ft long with 10% extra.
How far apart should deck joists be?
For 5/4 (1-1/4 in) wood decking laid square to the joists, the residential code allows up to 16 in on center when boards cross three or more joists, and 12 in for diagonal decking. 2 in thick wood decking can span 24 in. Composite decking follows the manufacturer's span rating, often 16 in.
How many screws per deck board?
Two at every joist. For a board crossing 13 joists, that is 26 screws. Composite decks often use hidden fasteners instead, one clip per joist crossing.
Do I need a permit for a deck?
Usually yes. The model residential code exempts only small decks: under 200 sq ft, no more than 30 in above grade, not attached to the house and not serving a required exit door. Decks more than 30 in above the ground also need a guard at least 36 in high.
How much does a deck cost to build?
See our deck building cost guide for installed prices by size, material and state.
What is the 3-4-5 rule for decks?
It is how builders check that a corner is square. Measure 3 ft along one side and 4 ft along the other; if the diagonal between the two marks is exactly 5 ft, the corner is 90 degrees. On larger decks use 6, 8 and 10 ft or 9, 12 and 15 ft for more accuracy.
How many balusters do I need for a deck railing?
The gaps must stop a 4 in ball (IRC R312.1.3), so with 2 × 2 balusters plan on gaps of about 3.5 in. For 30 ft of railing with posts no more than 6 ft apart, that is 6 posts and 65 balusters; 40 ft takes 8 posts and 91 balusters. Add a post at every corner and at each side of the stairs.
How we calculated this
Board widths and gaps follow common lumber sizes and manufacturer instructions; joist spacing and fastening follow the International Residential Code. We test the calculator against 312 worked examples, checked with a separate program. Sources.
A material estimate, not a structural design. Beam, post and footing sizes depend on your spans and local code.
Changelog
- : Published.
- : Formulas checked against 312 worked examples, verified with a separate program.
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