How many deck boards do I need?
Updated April 26, 2026
Quick answer
Deck boards by deck size
| Deck size | Boards (rows × length) | Linear feet | Best stock |
|---|---|---|---|
| 8 × 10 | 22 boards × 8 ft | 176 lf | 8 ft or 16 ft (cut to 8) |
| 10 × 12 | 22 boards × 10 ft | 220 lf | 12 ft (trim to 10) |
| 12 × 12 | 26 boards × 12 ft | 312 lf | 12 ft |
| 12 × 16 | 26 boards × 16 ft | 416 lf | 16 ft |
| 12 × 20 | 26 boards × 20 ft | 520 lf | 20 ft (or 52 × 12) |
| 14 × 18 | 30 boards × 18 ft | 540 lf | 20 ft (trim to 18) |
| 16 × 20 | 35 boards × 20 ft | 700 lf | 20 ft |
| 20 × 20 | 44 boards × 20 ft | 880 lf | 20 ft |
Counts assume boards run perpendicular to the long side. Add 10% waste for cuts; 15% for diagonal boards or any cutout (stairs, hot tub, post wraps).
Formula
Board count formula
board_width_in = 5.5 (5/4 × 6 nominal) gap_in = 0.125 spacing_in = board_width_in + gap_in = 5.625 rows = ceil( deck_width_in / spacing_in ) boards = rows × ceil(deck_length_ft / board_length_ft) order = ceil( boards × 1.10 ) // +10% waste
Worked example
14 × 20 ft deck with picture-frame border
Composite, ⅛-in gaps, 4-board picture frame around the perimeter.
- 1. Inner field = 13 × 19 (1 board removed each side)247 sqft
- 2. Field rows = 156 / 5.62528
- 3. Field boards × 19 ft28 boards
- 4. Perimeter border (long side runs)4 boards
- 5. + 12% waste (mitered cuts)Total: 36 boards
→ 36 × 20 ft composite boards (28 field + 4 border + waste).
Pick the right board length
Use the longest board that fits in one piece. Joints in the middle of the deck collect water and look bad, and every joint means an extra blocking piece between joists. If your deck is 14 feet wide, buy 16-foot boards and trim, not 12-footers butt-jointed.
| Length | Best for | Stock availability | Price premium |
|---|---|---|---|
| 8 ft | Short decks, stairs, repairs | High | Lowest /lf |
| 12 ft | Decks up to 12 ft span | High | Standard |
| 16 ft | Most residential decks | High | Standard |
| 20 ft | Large decks, no joints | Medium | +10–15% |
Picture frame border math
A picture-frame border (boards running around the perimeter) adds elegance but requires blocking between joists on the outermost row to support the cuts. Add 4 perimeter boards plus ~12% extra field boards for the cuts where field meets border. For mitered corners, double the waste at corners, bring 2 extra boards just for corner cuts.
How many fasteners come with the boards?
None, figure on ~20 screws per 16 ft board at 16 in OC, or roughly 1 box of 350 screws per 18 boards. For hidden-fastener composites (Trex hideaway, etc.), the clip count is on the brand's coverage chart, usually 1 clip per linear foot.
Common mistakes (and how to avoid them)
✗ Butt-jointing 12-ft boards on a 14-ft wide deck.
Fix: Buy 16-ft boards and trim. Joints in the middle of the deck collect debris, hold water, and look like a repair patch. The 10% premium for longer boards is cheap.
✗ Ordering exact count with no waste.
Fix: Always 10% extra for straight perpendicular layouts, 15% for diagonals, 20% for picture frames or curved cuts. Returns work; mid-install shortages don't.
✗ Calculating board count using 6 in nominal width.
Fix: 5/4 × 6 boards are 5.5 in actual. Composite varies by brand (5.4 to 5.5). A 0.1 in error per row × 30 rows = 3 in short on a deck.
✗ Mixing wood from different stock for one deck.
Fix: Color and grain consistency matter. Buy your full count from one shipment. PT mixed across batches will dry differently and look uneven.