Deck materials calculator — boards, joists & fasteners
A deck’s bill of materials comes from two numbers: board rows across the width (5.5-in board + ¼-in gap) and joists every 16 in along the length. A 12 × 16 ft deck takes 29 boards, 13 joists, and ~680 screws. Enter your size for the full list and August 2026 cost ranges.
Your materials list
Counts cover the walking surface and its joists. Beams, posts, footings, railings, and stairs depend on height and layout — and joist/beam sizing is a local-code span-table question, not a calculator question.
Common deck sizes, worked out
All rows: 16-in joist spacing, boards run the long dimension, 10% board waste.
| Deck | Deck boards | Joists | Screws | |
|---|---|---|---|---|
| 10 × 10 ft | 24 @ 10 ft | 9 @ 10 ft | ≈380 | Open › |
| 10 × 12 ft | 24 @ 12 ft | 10 @ 10 ft | ≈420 | Open › |
| 12 × 12 ft | 29 @ 12 ft | 10 @ 12 ft | ≈520 | Open › |
| 12 × 16 ft | 29 @ 16 ft | 13 @ 12 ft | ≈680 | Open › |
| 12 × 20 ft | 29 @ 20 ft | 16 @ 12 ft | ≈830 | Open › |
| 16 × 20 ft | 38 @ 20 ft | 16 @ 16 ft | ≈1,090 | Open › |
How this calculator works
Boards: rows = width ÷ 5.75 in (5.5-in actual board + ¼-in gap), rounded up; count = rows × 1.10 waste, as boards the length of the deck. Joists: (length × 12 ÷ spacing) + 1, each spanning the width; ledger and rim call for 2 × length of matching stock. Screws: rows × joists × 2. Costs: installed ranges — pressure-treated $15–$35/sq ft (typical market estimate), composite $35–$70/sq ft (2026 cited; composite boards alone run $4–$16/sq ft in materials). Source: HomeGuide 2026 composite decking data. Framing sizes are governed by local code span tables.
Common questions
How many deck boards do I need for a 12×16 deck?
With standard 5.5-in boards and a ¼-in gap, a 12 ft-wide deck takes 26 board rows; at 16 ft long with 10% waste that is 29 sixteen-foot boards (≈460 lineal feet). Running boards the long way looks best and minimizes butt joints.
How far apart do deck joists go?
16 inches on-center is standard for wood decking laid perpendicular. Most composite brands also allow 16 in for perpendicular boards but require 12 in for diagonal layouts — check your board’s span chart, and your local code for joist sizing.
How many screws does a deck take?
Two per board at every joist crossing — roughly 3.5 screws per square foot at 16-in spacing. A 12×16 deck (192 sq ft) needs ~680 deck screws, or the same count of hidden clips for grooved composite boards.
How much does a deck cost in 2026?
Installed: pressure-treated wood roughly $15–$35/sq ft; composite $35–$70/sq ft. A 12×16 deck: ~$2.9k–$6.7k in wood, $6.7k–$13k in composite. Railings, stairs, and height add real money beyond these base ranges.
What size joists does a deck need?
Commonly 2×8s for spans up to ~12 ft at 16-in spacing, 2×10s beyond — but joist sizing is governed by species, grade, and your local code’s span tables. This calculator counts joists; a permit drawing sizes them.