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Deck Calculator: Full Material Takeoff
Enter your deck dimensions and get a complete bill of materials — decking boards, joists, rim boards, posts and footings, screws, and railing balusters. Every count is rounded up and the full arithmetic is shown so you can check it yourself. The math runs entirely in your browser.
By HowMuchBuild Editorial TeamCalculation reviewedUpdated October 2026
ft
in
ft
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Both have a 5.5″ face, so the board count is the same — the 2×6 is thicker and stiffer.
16″ OC is standard for decking run perpendicular to joists.
Pieces are rounded up from total linear feet — plan for offcuts and butt joints.
0 if no railing — stairs excluded
2 is typical for a ledger + outer beam
Estimated cost
What will it cost?
Enter your local store prices — prices vary by region.
Decking boards
21 boards
—
Joists
9 pieces
—
Rim boards
4 boards
—
Posts
6 posts
—
Estimate — prices vary by store and region. Check your local store for current pricing.
Material takeoff
21
decking boards
9
joist pieces
4
rim boards
6
posts + footings
420
deck screws
48
rail balusters
Pieces are rounded up and include no cutting waste — add ~10% for offcuts and butt joints on the decking.
| Material | Total lin. ft | Pieces |
|---|---|---|
| Decking (21 rows) | 252.0 ft | 21 |
| Joists (10) | 100.0 ft | 9 |
| Rim / band boards | 44.0 ft | 4 |
| Posts (3/row × 2 rows) | — | 6 |
How we calculated it
- Board rows = ⌈120″ ÷ (5.5″ + 0.25″ gap)⌉ = ⌈20.87⌉ = 21
- Decking = 21 rows × 12.00 ft = 252.0 lin ft → ⌈252.0 ÷ 12⌉ = 21 boards
- Joists = ⌊144″ ÷ 16″⌋ + 1 = 10 joists × 10.00 ft = 100.0 lin ft → 9 pieces
- Rim boards = 2 × (12.00 + 10.00) = 44.0 lin ft → 4 pieces
- Posts = 2 rows × (⌈144″ ÷ 96″⌉ + 1) = 2 × 3 = 6 posts; footings = 1 per post = 6
- Screws = 21 boards × 10 joists × 2 = 420 screws
- Pickets = ⌈240″ ÷ (1.5″ + 3.5″ gap)⌉ = 48 balusters
Code check: joist, beam, and footing spans and sizes vary with lumber species, load, soil, and frost line, and this calculator does not size structural members — verify all framing with your local building department before you build. Baluster spacing follows the IRC 4-inch-sphere rule; confirm guardrail height and graspable-handrail requirements locally as well.
Worked example: 12×10 ft deck, 5/4×6 decking, 16″ joists
Boards run along the 12-ft length, joists spaced 16″ on center, stock lumber in 12-ft lengths, 20 linear feet of railing, 2 post rows. Step by step:
- Board rows: ⌈120″ ÷ (5.5″ + 0.25″ gap)⌉ = ⌈20.87⌉ = 21 rows
- Decking: 21 rows × 12 ft = 252 lin ft → ⌈252 ÷ 12⌉ = 21 boards
- Joists: ⌊144″ ÷ 16″⌋ + 1 = 9 + 1 = 10 joists, each 10 ft → 100 lin ft → 9 pieces (9 × 12 = 108 ft covers 100)
- Rim boards: 2 × (12 + 10) = 44 lin ft → ⌈44 ÷ 12⌉ = 4 pieces
- Posts: 2 rows × (⌈144″ ÷ 96″⌉ + 1) = 2 × 3 = 6 posts, and 6 footings (one per post)
- Screws: 21 boards × 10 joists × 2 = 420 screws
- Balusters: ⌈240″ ÷ (1.5″ + 3.5″ gap)⌉ = 48 balusters
Decking board reference
Coverage below assumes the typical ¼″ decking gap:
| Nominal board | Actual size | Face width + gap | Boards per ft of deck width |
|---|---|---|---|
| 5/4×6 | 1″ × 5.5″ | 5.75″ | 2.09 |
| 2×6 | 1.5″ × 5.5″ | 5.75″ | 2.09 |
Joists per 12 ft of run
| Joist spacing | Joists per 12 ft |
|---|---|
| 12″ OC | 13 |
| 16″ OC | 10 |
| 24″ OC | 7 |
Balusters by railing length (3.5″ gap)
| Railing length | Balusters |
|---|---|
| 10 ft | 24 |
| 20 ft | 48 |
| 30 ft | 72 |
| 40 ft | 96 |
The formulas
Decking boards
Rows = ⌈ width ÷ (5.5″ + gap) ⌉, where width is the deck dimension the boards cross. Pieces = ⌈ rows × run length ÷ stock length ⌉ — always round up; you can't buy part of a board.
Joists
Joists = ⌊ span ÷ spacing ⌋ + 1 — one joist at the start plus one at every spacing mark. Each joist is as long as the deck dimension it crosses; pieces round up from total linear feet.
Posts and footings
Posts per row = ⌈ length ÷ 96″ ⌉ + 1 — 8 ft is a typical maximum post spacing. Footings = posts, one for one.
Screws and balusters
Screws = boards × joists × 2 (typical face-screw fastening). Balusters = ⌈ railing length ÷ (1.5″ + 3.5″) ⌉ — the 3.5″ gap stays under the IRC 4-inch-sphere rule.
Frequently asked questions
How many deck boards do I need for a 12×10 deck?
With 5/4×6 decking (5.5″ face) and a ¼″ gap, a 12×10 ft deck needs 21 rows of boards across the 10-ft width (⌈120″ ÷ 5.75″⌉ = 21). At 12 ft per row that's 252 linear feet — twenty-one 12-ft boards before waste.
What are the actual dimensions of 5/4×6 decking?
A nominal 5/4×6 deck board is actually 1″ thick × 5.5″ wide. A nominal 2×6 deck board is actually 1½″ thick × 5.5″ wide. Both present the same 5.5″ face, so the board count is identical — the 2×6 is just thicker and stiffer.
Should I use 12″ or 16″ joist spacing?
16″ on center is the standard for decking run perpendicular to the joists. 12″ OC is typically used when boards run diagonally, for some composite decking, or under heavier loads. Spacing and joist span interact with your local code — verify before framing.
How many screws does a deck need?
Face-screwed decking typically takes 2 screws at every board-to-joist crossing. Total screws = deck boards × joists × 2. A 12×10 deck with 21 boards and 10 joists needs 420 screws — buy at least a small buffer over the count.
How far apart can deck posts be?
Keep post spacing at or under 8 ft as a typical maximum, and confirm with local code — post and beam spans depend on lumber species, load, and soil. The calculator above places posts at 8 ft max spacing.
What gap does code allow between deck balusters?
The International Residential Code requires that a 4-inch sphere cannot pass through a guardrail — so balusters must be spaced under 4″ apart. This calculator uses a 3.5″ gap with 1.5″ (2×2 actual) balusters for a code-friendly margin. Confirm guardrail height locally too.
How much extra decking should I buy for waste?
About 10% is a typical starting point for offcuts, butt joints, and the occasional bad board. Complex shapes, diagonal layouts, and picture-frame borders need more. The piece counts above include no waste — add your margin at purchase.
What this calculator doesn't size
Counting boards and screws is geometry; sizing the frame is engineering. Joist, beam, and footing spans and sizes depend on lumber species and grade, tributary load, soil bearing, and frost depth — plus your local building code, which has the final word. Use this page for the shopping list, then size the structure (or hire someone to) against your local code before you pour or frame anything.
Keep estimating