Deck Calculator
Deck boards, joists, and screws for a rectangular or L-shaped deck — counted the way the lumber yard sells them, with waste built in.
Material counts only — not a structural design. Joist sizes, spans, footing depths, ledger attachment, and railing loads are governed by code and by the AWC DCA 6 deck guide. Most jurisdictions require a permit and inspection for decks over 30″ high. Call 811 before digging piers.
Split the L into two rectangles; boards are counted per section.
You need
Enter dimensions
| Detail | Amount |
|---|---|
| Deck area | — |
| Linear feet (with waste) | — |
| Joists (16″ OC default) | — |
| Deck screws (2½″) | — |
Treated 5/4×6 commonly runs $0.80–$1.50/lin ft; composite $2.50–$5+.
What Will This Deck Cost to Build?
Board counts tell you what to buy; they don't tell you what the project costs. Pick your decking material and whether you're building it yourself or hiring it out, and this estimates the whole job from the deck size you entered above.
Contractor pricing includes labor, footings, and railing. DIY covers decking, framing, and fasteners — add footings, railing, and tool rental separately.
Estimated project cost
Enter deck dimensions above
| Detail | Amount |
|---|---|
| Cost per square foot | — |
| Labor portion | — |
National ranges for planning and sanity-checking a quote — not a bid. Your actual price depends on region, deck height, and site access.
What decks cost per square foot in 2026
| Material | DIY materials | Contractor installed | 12 × 16 ft deck, installed |
|---|---|---|---|
| Pressure-treated pine | $9–18/sq ft | $25–40/sq ft | $4,800–7,700 |
| Cedar / redwood | $14–25/sq ft | $30–55/sq ft | $5,750–10,550 |
| Composite | $20–38/sq ft | $45–85/sq ft | $8,650–16,300 |
Where the money actually goes
Labor is roughly 60% of a contractor-built deck — materials and supplies are the other 40%. That ratio is why a DIY build saves so much on paper, and why quotes for the same deck vary more by crew than by lumber choice.
- Height drives price fast. A ground-level deck is framing and boards. Once you're above 30″, you're into deeper footings, stair runs, guard rails, and an inspection — often thousands more on the same square footage.
- Footings are the hidden line item. Frost depth decides how deep piers go, and that varies from 12″ in the south to 48″+ in the north. Same deck, very different concrete bill — our concrete calculator sizes the pour.
- Composite costs more up front and less later. It runs roughly double treated pine installed, but skips the stain-and-seal cycle that wood needs every two to three years.
- Site access matters more than people expect. A back yard reachable only through a gate means every board is carried by hand, and crews price that in.
- Railing is priced separately by most builders — commonly $40–90 per linear foot installed, depending on whether it's wood, composite, or cable.
Using this to check a contractor's quote
Divide the bid by your deck's square footage and compare it to the table above. A treated-pine deck quoted at $60 per square foot deserves a question about what's included — it may be a tall deck with stairs and premium railing, which is legitimate, or it may be padded. A quote well under the range is worth just as much scrutiny: ask about footing depth and joist spacing before celebrating.
How to Calculate Decking
Deck boards are counted in rows across the width, then bought as linear feet (or whole boards at your deck's length):
- Rows: deck width in inches ÷ (board width + gap), rounded up.
- Linear feet: rows × deck length, plus 5–15% waste depending on the layout.
- Joists: deck length in inches ÷ spacing, rounded up, plus one.
- Screws: two per joist crossing — about 350 per 100 sq ft at 16″ spacing.
Decking formulas
Rows = ceil(width ÷ (board width + gap))
Linear ft = rows × length × (1 + waste)
Joists = ceil(length ÷ spacing) + 1
Worked example — 12 × 16 ft deck, 5.5″ boards, ¼″ gap: 144″ ÷ 5.75″ = 26 rows × 16 ft = 416 lin ft × 1.10 = 458 linear feet — 29 sixteen-foot boards, on 13 joists, with ~672 screws.
Boards Needed for Common Deck Sizes
5.5″ boards, ¼″ gap, 10% waste, boards run the long dimension:
| Deck size | Rows | Linear feet | Boards (at deck length) |
|---|---|---|---|
| 10 × 10 ft | 21 | 231 | 24 |
| 12 × 12 ft | 26 | 344 | 29 |
| 12 × 16 ft | 26 | 458 | 29 |
| 16 × 20 ft | 34 | 748 | 38 |
Tips Before You Buy
- Buy boards the length of your deck when possible — butt joints mid-span look patchy and need doubled joists.
- Crown side up, bark side down on wood boards; cup direction sheds water.
- Check your framing first. Composite decking on 24″ joists feels like a trampoline — most brands require 16″ or less.
- Hidden fasteners vs. screws: clips give a clean face but cost 2–3× and are slower; coated screws are the workhorse choice.
- Permits matter for decks. Most jurisdictions require them above 30″ height — the AWC DCA 6 guide is the standard reference inspectors use.
Frequently Asked Questions
How many boards for a 12×16 deck?
26 rows — 29 sixteen-foot boards with 10% waste (about 458 linear feet).
What gap between boards?
⅛–¼″; wet treated lumber can be butted tight since it shrinks. Composites: follow the manufacturer's spec.
How far apart are deck joists?
16″ on center standard; 12″ for diagonal decking and many composites; span limits per AWC DCA 6.
How many screws per board?
Two per joist crossing — roughly 350 per 100 sq ft, about 4.5 lb.
Which way should boards run?
Perpendicular to the joists — typically parallel to the house. Long-dimension boards make the deck look bigger.
Actual size of a 5/4×6?
About 1″ × 5.5″. A 2×6 is 1.5″ × 5.5″ — same coverage, stiffer feel.
How much does it cost to build a 12×16 deck?
Roughly $4,800–7,700 installed in treated pine, $5,750–10,550 in cedar, $8,650–16,300 in composite. DIY in treated lumber is about $1,750–3,450 in materials.
How much does a deck cost per square foot?
Installed: $25–40 treated pine, $30–55 cedar, $45–85 composite. DIY materials: $9–18 treated, $20–38 composite.
Is it cheaper to build a deck myself?
Usually by half or more — labor is about 60% of a contractor-built deck. You trade that for your time, tool rental, and handling the permit yourself.
References
- American Wood Council — DCA 6: Prescriptive Residential Wood Deck Construction Guide: awc.org
- Simpson Strong-Tie — deck framing and fastening guides: strongtie.com
- Trex — composite decking installation requirements: trex.com
- Cost ranges cross-checked against 2026 contractor pricing surveys from Angi, HomeGuide and Ergeon. National figures — regional prices vary widely.
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