Decking Calculator - Boards, Joists, Fasteners & Waste
Deck material depends on deck area, board width, board length, gaps, and joist spacing. The calculator estimates board rows, pieces, joists, fasteners, waste, and cost.
Percent added for cuts, waste, settlement, or field loss.
Cost uses estimated board pieces before extra hardware.
Change any value and the results, formula, and diagram update immediately. Use the same unit system throughout one estimate.
Deck Boards Quick Reference
Board pieces and joist counts for common deck sizes using 5/4 x 6 boards (5.5 in face, 1/8 in gap) and 16 in joist spacing. Use this for the lumberyard conversation; the calculator handles your real board and joist values.
| Deck size | Sq ft | Board rows | Joists | Linear ft of board | 16 ft boards (no waste) |
|---|---|---|---|---|---|
| 8 x 10 ft | 80 | 22 | 9 | 176 lf | 11 |
| 10 x 12 ft | 120 | 27 | 10 | 270 lf | 17 |
| 12 x 16 ft | 192 | 27 | 13 | 432 lf | 27 |
| 14 x 20 ft | 280 | 31 | 16 | 620 lf | 39 |
| 16 x 24 ft | 384 | 36 | 19 | 864 lf | 54 |
| 20 x 30 ft | 600 | 45 | 23 | 1,350 lf | 85 |
Multiply by 1.1 for typical waste, by 1.15 for diagonal layout, and by 1.2 for picture-frame or herringbone patterns. Fastener count is roughly board rows x joists x 2 (two screws per crossing).
How Deck Board Count Actually Works
Deck math is not deck area divided by board area. It is deck width divided by (board width + gap), rounded up, which gives the number of full board rows. Then deck length divided by stock length, rounded up, which gives the boards per row. Multiply.
Example: a 12 x 16 ft deck with 5.5 in boards and 1/8 in gap. The board module is 5.625 in. Deck width 12 ft = 144 in, divided by 5.625 = 25.6 - so 26 rows. Each row is 16 ft, so one 16 ft board per row = 26 boards. With waste, order 28 boards. If your stock is 12 ft instead of 16 ft, each row needs two boards (with a butt joint), so 52 boards total. Stock length matters as much as deck size.
Decking Material Types
Pressure-treated pine (PT)
The US residential default. Yellow-green colour fades to grey. 15-25 year service life. Cheapest. Smell of preservative until cured.
Cedar
Western red cedar - natural rot resistance, beautiful grain, lighter weight. Soft surface - dents under heavy furniture. 15-25 year life, longer if stained.
Redwood
California native. Similar to cedar with a deeper red tone. Increasingly rare and expensive outside the West Coast.
Tropical hardwoods (ipe, cumaru, garapa, tigerwood)
Very dense, 40-50 year life, almost rot proof, slow weathering to silver-grey. Hard to cut, hard to fasten, expensive.
Composite (Trex, TimberTech, Fiberon, Deckorators)
Wood fibre plus polymer. Looks like wood, never rots, no splinters. Capped composites have a polymer shell over the core. 25-50 year warranty.
PVC / all-plastic (Azek, Trex Transcend, TimberTech AZEK)
Zero wood content. Lightest weight, coolest underfoot among synthetics. Most expensive material per board, lowest maintenance.
Joist Sizing and Spacing
Joists carry the deck boards. Span tables (American Wood Council DCA-6) set the maximum unsupported joist length by lumber size and spacing.
| Joist size (SPF / DF / SP) | 16 in OC max span | 12 in OC max span | Typical use |
|---|---|---|---|
| 2x6 | 9 ft 8 in | 10 ft 8 in | Small deck, residential |
| 2x8 | 12 ft 8 in | 14 ft | Standard residential |
| 2x10 | 16 ft | 17 ft 8 in | Larger residential |
| 2x12 | 18 ft 9 in | 20 ft 8 in | Long-span or commercial |
Joist spacing also drives board choice: 5/4 x 6 PT pine wants 16 in spacing or tighter; composite often requires 12 in for diagonal layouts; tropical hardwood is dense enough to span 24 in. The calculator estimates joist count from deck width divided by spacing, plus one - check the actual span table for your code review.
Fasteners - Two Per Crossing, Plus Hidden Options
The simple count: board rows x joist count x 2 screws per crossing. A 12 x 16 deck with 26 rows and 13 joists needs 26 x 13 x 2 = 676 screws. Add 10% for dropped, stripped, or extra-edge screws. That is two 350-count boxes.
- Stainless steel screws: required for composite and PVC, recommended for cedar and tropical hardwood. Cost: $25-45 per 350-count box.
- Coated deck screws: ACQ-rated for pressure-treated lumber. Cost: $15-30 per box.
- Hidden fasteners (clips): CAMO, Tiger Claw, Trex Universal. Slot into grooved board edges. About 1 clip per joist per board, with one $20-40 box per 100 sq ft of deck.
- Plug system: screw-and-plug for solid composite boards. Looks clean but slow to install.
Cost Estimates Around The World
2026 retail material prices for deck boards only. Joists, beams, posts, footings, railing, stairs, and labour are separate. Composite numbers include the price premium for capped lines.
| Region | Pressure-treated pine | Cedar / redwood | Composite (capped) | Hardwood (ipe / cumaru) | Installed (full deck) |
|---|---|---|---|---|---|
| United States (USD) | $2-4 / lf | $3-7 / lf | $4-9 / lf | $5-12 / lf | $25-50 / sq ft |
| Canada (CAD) | C$3-6 / lf | C$4-9 / lf | C$6-12 / lf | C$8-16 / lf | C$35-70 / sq ft |
| United Kingdom (GBP) | £3-6 / m | £6-12 / m | £10-22 / m | £15-30 / m | £120-280 / m² |
| Eurozone (EUR) | €4-8 / m | €8-16 / m | €12-25 / m | €18-35 / m | €140-320 / m² |
| Australia (AUD) | A$5-10 / m | A$10-20 / m | A$18-40 / m | A$25-55 / m (merbau) | A$280-650 / m² |
| India (INR) | ₹150-350 / sq ft | ₹350-700 / sq ft | ₹400-900 / sq ft (WPC composite) | ₹800-2,500 / sq ft (teak / ipe) | ₹1,200-3,500 / sq ft |
| Mexico (MXN) | MX$60-130 / m | MX$130-280 / m | MX$220-480 / m | MX$320-700 / m | MX$2,800-7,500 / m² |
| Philippines (PHP) | PHP 150-350 / m | PHP 350-750 / m (yakal, narra) | PHP 500-1,400 / m | PHP 900-2,200 / m | PHP 4,500-12,000 / m² |
Brand reference: US - Trex, TimberTech, Fiberon, Azek, Deckorators, MoistureShield; UK / EU - Millboard, Composite Prime, Trex Europe; Australia - Modwood, ExoDeck, Boral. Tropical hardwood suppliers: ipedepot.com (US), Brazilian Lumber Wholesale, BCC Hardwoods (UK). A two-person crew installs about 150-300 sq ft of deck per day with prepared framing.
Common Mistakes
- Forgetting the gap between boards - it adds up to one extra row per 6 ft of width.
- Buying 16 ft boards for a 14 ft deck - you waste 2 ft per board. Order 14 ft stock instead.
- Using PT screws on composite or hardwood - corrosion stains within months. Use stainless.
- Skipping joist span tables and using a 2x6 over 12 ft - bouncy deck.
- Installing composite at 16 in joist spacing for a diagonal layout - boards sag between joists. Tighten to 12 in.
- Picture-frame border without picture-frame waste allowance - typically adds 10-15% to material.
- Treating deck area as the only cost - joists, beams, posts, footings, ledger flashing, and railing are each their own line items.
- Not pre-drilling tropical hardwood - it splits the ends of every board.
Decking Calculator FAQ
How many deck boards do I need for a 12 x 16 ft deck?
With 5/4 x 6 boards (5.5 in face) and 1/8 in gap, board module is 5.625 in. Deck width 144 in / 5.625 = 26 rows. Each row at 16 ft long uses one 16 ft board if stock matches. So 26 boards, plus 10% waste = 29 boards. Joists: 12 ft / 16 in spacing = 9 joists, plus 1 end joist = 10. Fasteners: 26 x 10 x 2 = 520 screws (one 500-count box plus a small box).
How much gap should I leave between deck boards?
For pressure-treated lumber installed wet: 1/8 in gap (it shrinks as it dries). For dry kiln-dried wood: 1/4 in gap. For composite and PVC: follow the manufacturer - usually 3/16 in end-to-end and 1/4 in side-to-side, but some products want zero gap because they do not expand.
What joist spacing should I use?
16 in on-centre is the residential default for most wood and composite decks. Tighten to 12 in for composite installed diagonally, or for thin (1 in nominal) boards. Tropical hardwood at 1 in thick can span 24 in. Always check the board manufacturer's spec.
What size joist for a 14 ft deck span?
2x10 at 16 in OC spans 14 ft in SPF (Douglas fir is slightly stronger). 2x8 maxes out at 12 ft 8 in at 16 in OC. Larger spans need 2x12 or doubled joists. Always cross-check with American Wood Council DCA-6 or your local code.
How many screws per square foot of deck?
Roughly 5-6 screws per square foot for 16 in joist spacing and 5.5 in boards. A 192 sq ft deck typically needs 1,000-1,200 screws. Hidden clip systems use about 1 clip per joist per board (3-4 per sq ft).
Composite vs wood - which lasts longer?
Composite warranties run 25-50 years on the cap, often with a separate fade-and-stain warranty. Wood decks last 15-25 years (PT, cedar) or 30-50 years (tropical hardwood) with regular sealing. Composite has higher upfront cost but lower maintenance.
Do I need a permit for a deck?
In the US: usually yes for any deck over 30 in above grade or attached to a house. In the UK: permitted development for decks under 30 cm above ground; planning permission for higher. India: residential decks under a roof slab generally do not need permit; freestanding structures do. Always check local jurisdiction.
How far apart should deck posts be?
Typically 6 to 8 ft on centre, depending on beam size. A doubled 2x10 beam can span 8 ft between 6x6 posts in residential decks. Beam-and-post sizing is in DCA-6 tables. Footings under each post must extend below frost depth.
How long does deck installation take?
A 200 sq ft simple deck: 2-3 days for two experienced framers (footings, framing, decking, railing). A 500 sq ft deck with steps, picture-frame, and complex railing: 5-7 days. Composite deck installations average 1-2 days longer than wood because of fasteners.
What is the cost of a 200 sq ft deck?
US installed totals for 200 sq ft: PT pine $4,500-7,000, cedar $6,000-9,000, composite $7,500-12,000, tropical hardwood $10,000-16,000. Add $1,000-3,000 for railings and steps. UK: £4,000-15,000 for the same range. India: ₹200,000-700,000 depending on material.
Related Construction Calculators
For raw lumber board-foot math, use the Lumber Calculator. For railings or fence components, see the Fence Calculator. Footings under posts live in the Footing Calculator and Concrete Calculator. For stairs off the deck, the Stair Calculator handles riser and tread layout. More tools live on the Construction Calculators hub.
Sources
- American Wood Council - design resources and span tables
- AWC DCA-6 Prescriptive Residential Wood Deck Construction Guide
- Trex composite decking technical guides
- TimberTech professional installation resources
- Professional Deck Builder magazine technical archive
- NIST Handbook 44 unit conversion tables
This calculator is for planning and ordering conversations. Local code, project drawings, engineered design, and manufacturer instructions control the final work.