How many deck boards for a 10×20 deck?
With 5 1/2″ boards and a 3/16″ gap, a 20 × 10 ft deck takes 22 rows — 22 boards of 20′, 24 with 10% waste. Change the board, gap or framing below.
Deck size & framing
Decking
Railing
The IRC requires that a 4″ (102 mm) sphere cannot pass through a guard; a 3 1/2″ target leaves room for shrinkage. Other countries use different limits — check yours.
Span check (reference table)
- Joist span (2×8 at 16″ o.c.): 10′ vs. table maximum 11′ 10″ — within the table
- Beam span between posts (2-ply 2×8): 6′ vs. table maximum 6′ 9″ — within the table
Source: City of Alexandria, VA — Typical Deck Details, Based on International Residential Code (Tables 1 and 2). Basis: Southern pine No. 2, 40 psf live load + 10 psf dead load, wet service, deflection L/360. Other species and grades span less; snow loads, hot tubs and planters need engineering. Spans are measured between bearing centrelines.
Lumber to buy
| Item | Size | Length | Net | Buy |
|---|---|---|---|---|
| Joists | 2×8 | 10′ | 16 | 18 |
| Rim joists | 2×8 | 20′ | 1 | 1 |
| Ledger | 2×8 | 20′ | 1 | 1 |
| Beam plies | 2×8 | 20′ | 2 | 2 |
| Blocking | 2×8 | 8′ | 3 | 3 |
| Posts | 6×6 | 8′ | 1 | 1 |
| Deck boards | deck board | 20′ | 22 | 24 |
Hardware & fasteners
| Joist hangers (at ledger) | 16 |
| Hurricane ties / joist-to-beam connectors | 16 |
| Post bases (one per post) | 4 |
| Footings | 4 |
| Deck screws (2 per board per joist) | 740 |
| or hidden fastener clips (1 per board per joist) | 370 |
Screw count: 2 per board at every joist plus 2 at each butt joint, +5%. Ledger fastening, footing size and post bases come from your local code. Posts: 20 1/2″ above the footing to the underside of the beam (deck height minus decking, joist and beam depth).
Deck boards by length
| Board length | Boards | Total length |
|---|---|---|
| 8′ | 66 | 528 ft |
| 10′ | 44 | 440 ft |
| 12′ | 44 | 528 ft |
| 14′ | 44 | 616 ft |
| 16′ | 44 | 704 ft |
| 18′ | 44 | 792 ft |
| 20′ · least material | 22 | 440 ft |
22 rows of 5/4×6 wood (5 1/2″) with a 3/16″ gap cover 10′. Without waste. Stagger butt joints and land every joint on a joist.
Planning estimate only. Joist, beam, post, footing, ledger and guard requirements depend on loads, species, grade and your local building code. Verify with your building department or a licensed professional before you buy or build.
Boards by length
| Board length | 5 1/2″ boards (22 rows) | 3 1/2″ boards (33 rows) |
|---|---|---|
| 8′ | 66 | 99 |
| 10′ | 44 | 66 |
| 12′ | 44 | 66 |
| 14′ | 44 | 66 |
| 16′ | 44 | 66 |
| 18′ | 44 | 66 |
| 20′ · least waste | 22 | 33 |
Boards run along the 20 ft side, across joists 16″ on center. Rows = (120 + 3/16) ÷ (5 1/2 + 3/16) = 21.13 → 22.
Fasteners and framing
- Deck screws: 740 (2 per board per joist, +5%) — about 3.5 per sq ft.
- Hidden clips: about 370.
- Joists: 16 at 16″ on center, 117″ long for an attached deck (ledger + rim).
Joist size depends on span, species and spacing — see the span reference or plan the framing in the deck calculator. Other sizes: 8x8, 8x10, 10x10, 10x12, 12x12, 12x16, 16x16.
Planning estimates only. Stud counts and lumber lists are for budgeting and ordering. Structural sizes — headers, joists, beams, posts, footings, ledgers and guards — must follow your local building code. Verify with your building department or a licensed professional before you build.
FAQ
How many deck boards for a 10×20 deck?
22 boards of 20′ (24 with 10% waste) with 5 1/2″ boards and 3/16″ gaps: 22 rows across 10 ft, boards running the 20 ft way.
How many screws for a 10×20 deck?
About 740 deck screws at 16″ joist spacing: 2 per board at each of 16 joists, plus 5%. Hidden fasteners: about 370 clips.
How many joists for a 10×20 deck?
16 joists at 16″ on center across 20 ft (21 at 12″, 11 at 24″). Joist size depends on span — see the span table in the deck joist guide.