How to use this calculator
- Enter deck dimensions. Length × width in feet. The calculator handles rectangular decks; for L-shaped decks, run two passes.
- Pick board width and length. 5/4 × 6 (5.5" actual) is the most common deck board. Lengths 8, 10, 12, 16 ft. Pick the longest length that minimizes seams.
- Add prices (optional). Enter price per board and per joist. Get total estimate including framing, fasteners, and concrete for posts.
- Read your bill of materials. Decking boards (with waste), floor joists, beams, support posts, concrete bags, and total estimate.
Formula
Boards = Length ÷ (Board Width / 12) × Rows + 10% waste
Worked example
A 16 × 12 ft deck with 5.5" wide × 12 ft long boards: 35 decking boards (with 10% waste), 14 joists at 16" OC, 4 posts, 8 concrete bags. At $12/board, $24/joist, $6.50/bag: about $760 in lumber + $52 in concrete = $812 in materials.
Common project sizes
Quick reference for the most common deck calculator use cases. Use these as a sanity check on your calculator inputs.
| Project | Dimensions | Result |
|---|---|---|
| 12 × 12 ft deck | 144 ft² | ~28 boards · 11 joists · 4 posts |
| 16 × 12 ft deck | 192 ft² | ~35 boards · 14 joists · 4 posts |
| 20 × 16 ft deck | 320 ft² | ~58 boards · 17 joists · 6 posts |
| 24 × 16 ft deck | 384 ft² | ~70 boards · 19 joists · 6 posts |
2026 cost reference
Typical retail price range in the United States for deck. Local pricing varies by region, supplier, and grade — confirm with two or three quotes before ordering.
Per square foot (installed)
$25 – $80
Pressure-treated pine: $25–$45/ft² installed. Cedar: $35–$55. Composite (Trex, TimberTech): $45–$80/ft². Add 30% for elevated decks, multi-level designs, or built-in seating.
Tips for accurate results
- Composite decking (Trex, TimberTech) is 2.5–3.5× the price of pressure-treated pine but lasts 25–30 years vs 12–15.
- Use ground-contact rated lumber for any joist within 6 inches of soil. Standard PT only carries an above-ground rating.
- Joists 16" on center for residential. 12" OC for hot-tub or heavy load areas. Always check local code.
- Order 5–10% extra on framing and 10–15% extra on decking. Damaged ends and bad cuts add up.
- Hidden fasteners (Camo, Trex) double the labour but eliminate visible screw heads. Check whether your deck board is grooved for them.
When to consult a pro
Decks are workable DIY for ground-level builds at standard heights. Anything elevated (>30" off grade) or multi-story requires permitting and inspection in most jurisdictions, and structural calculations get nuanced. Hire a pro for: rooftop/balcony decks, pool decks (waterproofing), spans over 12 ft, and any deck that supports more than people (hot tubs, planters, outdoor kitchens).