How much decking is really wasted?
We laid out 21 common deck sizes board by board, the way a builder would: real stock lengths, every joint on a joist, staggered rows and offcuts reused. Then we measured the waste and compared it with the “area ÷ board + 10%” shortcut most calculators use.
What this is, and isn’t: these are computer-modelled layouts, not measurements from real job sites. They show the waste built into each plan before anything is cut. Real decks add defects, miscuts and on-site changes on top, which is why we still recommend a few spare boards.
Median waste: 11.7% seamless, 8.0% staggered
With 12, 16 and 20 ft boards. Allowing staggered butt seams saved at least 8% of the board length bought on 10 of 21 sizes.
The area shortcut came up short on 19 of 21 sizes
With only 12 and 16 ft boards on the rack, “area ÷ 16 ft board + 10%” bought less board length than the deck actually needs on 19 sizes. Even with its 10% padding, the shortcut assumes every inch of every board gets used.
A 16 ft deck rarely fits 16 ft boards
With a ¾″ overhang each side and a trim cut, a row on a 16 ft deck needs about 16′-2½″. The worst seamless case was the 8×12 deck at 24.2% waste. Framing the deck at 15′-9½″ removes most of it.
Waste by deck size
Composite boards, 5½″ wide with 3/16″ gaps, ¾″ overhang on three sides, joists at 16″ on center, a 1″ trim allowance per piece, and offcuts under 12″ treated as scrap. No spare boards are included, so these are pure layout figures. Sizes read as “out from the house × along the house”, with boards running along the second number.
| Deck | Area | Waste: seamless vs staggered (12/16/20 ft) | Seamless | Staggered | 16 ft only | Area method vs real (12/16 ft) |
|---|---|---|---|---|---|---|
| 8×8 | 64 ft² | 18.8% | 10.8% | 8.6% | 160 vs 168 lf short | |
| 8×10 | 80 ft² | 15.6% | 5.1% | 12.4% | 192 vs 200 lf short | |
| 8×12 | 96 ft² | 24.2% | 5.9% | 24.2% | 224 vs 252 lf short | |
| 10×10 | 100 ft² | 15.6% | 7.2% | 13.0% | 240 vs 244 lf short | |
| 10×12 | 120 ft² | 24.2% | 8.6% | 24.2% | 288 vs 308 lf short | |
| 10×14 | 140 ft² | 11.7% | 7.5% | 11.7% | 336 vs 344 lf short | |
| 10×16 | 160 ft² | 19.4% | 8.6% | 17.9% | 384 vs 396 lf short | |
| 10×20 | 200 ft² | 8.5% | 8.5% | 13.5% | 480 vs 484 lf short | |
| 12×12 | 144 ft² | 24.2% | 8.4% | 24.2% | 336 vs 364 lf short | |
| 12×14 | 168 ft² | 11.7% | 7.3% | 11.7% | 400 vs 412 lf short | |
| 12×16 | 192 ft² | 19.4% | 9.6% | 18.1% | 448 vs 468 lf short | |
| 12×18 | 216 ft² | 9.4% | 8.0% | 8.0% | 512 vs 512 lf | |
| 12×20 | 240 ft² | 8.5% | 8.5% | 11.6% | 560 vs 572 lf short | |
| 12×24 | 288 ft² | 7.2% | 7.8% | 12.9% | 672 vs 712 lf short | |
| 14×14 | 196 ft² | 11.7% | 6.3% | 11.7% | 464 vs 468 lf short | |
| 14×16 | 224 ft² | 19.4% | 7.0% | 16.0% | 528 vs 540 lf short | |
| 14×20 | 280 ft² | 8.5% | 8.5% | 12.2% | 656 vs 660 lf short | |
| 16×16 | 256 ft² | 19.4% | 8.0% | 16.4% | 608 vs 612 lf short | |
| 16×20 | 320 ft² | 8.5% | 8.5% | 12.7% | 752 vs 748 lf | |
| 16×24 | 384 ft² | 7.2% | 6.8% | 11.6% | 896 vs 928 lf short | |
| 20×20 | 400 ft² | 9.1% | 9.1% | 12.8% | 944 vs 952 lf short |
seamless rows (one board per row where possible) · staggered seams over doubled joists (“least waste”). Download the full dataset (CSV, all 6 scenarios).
What this means if you are buying decking
- Check your row length against your longest board. If a row is even an inch too long for your boards, every row costs you a longer board or a seam. Our board calculator shows the exact row length.
- Price both layouts. Seamless rows look cleaner. Staggered seams often buy noticeably less board but add doubled joists. Neither is “right”, so compare the cost.
- Don’t trust a flat 10%. Across these sizes, real waste ranged from 5.1% to 24.2%. A flat allowance over-buys on some decks and runs short on others.
Method
Each deck was laid out with Deckwright’s open methodology: rows across the joists, butt joints only on joist centerlines, joints never shared with the previous two rows, and pieces packed into the available lengths with a cutting-stock heuristic that reuses offcuts. Waste is (board length bought − board length installed) ÷ board length bought, for the modelled layout. It is not observed site waste. The area method is ⌈area ÷ (5 11/16″ × 16 ft) × 1.1⌉ boards of 16 ft. Full details are in the methodology.
Use this data
You may quote and reuse these figures with attribution under CC BY 4.0. Suggested citation:
Deckwright (2026). “Deck Board Waste Study: How Much Decking Is Wasted?” https://deckmaterialplanner.com/research/deck-board-waste-study/