Deck Calculator
How much will your deck cost — and how many boards? Estimate board count, joists, posts, footings, and cost for pressure-treated, cedar, composite, and PVC decking.
Deck Details
Pressure Treated · 5/4×6" · $3.5/sq ft · 10-15 years · high maintenance
Ready to calculate
Select a material and enter dimensions
Last updated June 23, 2026 by our expert review team
How Much Does a Deck Cost by Size?
Typical installed cost (materials + labor) by deck size. Pressure-treated is cheapest up front; composite costs about 2× but skips staining and lasts 25+ years. The calculator above estimates your materials — add labor for the installed figure.
| Deck size | Area | Pressure-treated | Composite |
|---|---|---|---|
| 10×10 ft | 100 sq ft | $1,500–2,500 | $3,500–5,000 |
| 12×12 ft | 144 sq ft | $2,200–3,600 | $5,000–7,200 |
| 12×16 ft | 192 sq ft | $2,900–4,800 | $6,700–9,600 |
| 16×16 ft | 256 sq ft | $3,800–6,400 | $9,000–12,800 |
| 20×20 ft | 400 sq ft | $6,000–10,000 | $14,000–20,000 |
Installed ranges ≈ $15–25/sq ft pressure-treated and $35–50/sq ft composite (US averages; railings, stairs, height, and demolition push higher). Use the calculator for an exact material list.
Deck Material Comparison
Pressure Treated
5/4×6" · 10-15 years
$3.5/sq ft
High upkeep
Cedar
5/4×6" · 15-20 years
$6/sq ft
Medium upkeep
Composite Standard
1"×5.5" · 25-30 years
$8/sq ft
Low upkeep
Composite Premium
1"×5.5" · 30-50 years
$13/sq ft
Very Low upkeep
PVC
1"×5.5" · 25-30 years
$10/sq ft
Very Low upkeep
Expert Contributors
Ehsan Ghazanfari
Licensed Structural Engineer
FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.
See full profileCherry Jane Limbago
Licensed Civil Engineer & Master Plumber
Licensed civil engineer and master plumber with 10+ years in structural design, estimation, and project management. Currently Project Engineer at Universal Robina Corporation.
See full profileUpdated June 2026
How we verify our calculatorsDeck Material Takeoff Guide
Deck material lists are more than square footage. Boards, joists, posts, footings, railing, stairs, and cut waste all change the order.
Straight wood boards
16" OCTypical layout with 10% waste.
Diagonal or picture-frame
12" OCMore cuts and tighter support.
Composite resurfacing
check frameOld 24 inch framing often needs extra joists.
Pro Tips
Use 16" OC joists for most straight decking. Drop to 12" OC for diagonal composite layouts, matching Trex joist guidance.
Use ACQ-rated structural screws and connectors with pressure-treated lumber. Plain fasteners corrode quickly outdoors.
Run joist tape before decking boards go down. It is cheap insurance for the framing you will not see again.
Flash the ledger before fastening it to the house. Water behind a ledger is a deck failure problem, not a cosmetic problem.
Keep a drainage gap between deck boards. Wood swells, composite moves with temperature, and water needs somewhere to go.
Use the concrete cylinder calculator for round footings and the stair calculator before framing stair openings.
For beam spans, check the beam calculator before ordering lumber.
How the Calculator Works
Start with deck size, height, and material. The calculator turns that footprint into deck boards, joists, posts, concrete bags, railing, stairs, and cost.
Board count uses a 5.5" board plus a 1/8" drainage gap. Straight layouts add 10% waste. Diagonal layouts add 15% because cutoffs are harder to reuse.
- Joists follow your spacing. The calculator uses 12", 16", or 24" on-center spacing to estimate the frame.
- Posts are conservative. It assumes about 8 ft between posts, then adds concrete bags for each footing.
- Height changes add-ons. Raised decks usually need railing, stairs, more posts, and more labor.
Calculate Area
Area = Length x Width (+ secondary section if L-shape)
Board Count
Rows = ceil(width_in / 5.625) x boards/row x (1 + waste%)
Framing & Footings
Joists = floor(length_in / spacing) + 1 | Posts = ceil(length / 8) + 1
Key Formulas
Boards = ceil(width_in / 5.625) x ceil(length / board_len) x (1 + waste)
Joists = floor(length_in / joist_spacing) + 1
Concrete bags = posts x 3 (80lb each)
Stair steps = round(height_in / 7.5)
Joist Span Reference
- 2x6 @ 16" OC
- 9' 9" span
- 2x8 @ 16" OC
- 13' 1" span
- 2x10 @ 16" OC
- 16' 2" span
- 2x12 @ 16" OC
- 18' 0" span
- Beam: dbl 2x8
- up to 8'
- Beam: dbl 2x10
- up to 10'
- Beam: dbl 2x12
- up to 12'
Frequently Asked Questions About Deck Building
How much does a deck cost per square foot?
Materials often run $9 to $20 per sq ft before labor, depending on decking. Installed pricing is usually much higher because framing, railing, stairs, and site work add up.
Is composite decking worth it?
It can be if you plan to keep the deck long-term. Composite costs more upfront but avoids regular staining and board replacement.
How many deck boards do I need?
Board count depends on deck width, board width, board length, gap, and waste. This calculator uses 5.5 inch boards plus a 1/8 inch gap.
How far apart should deck joists be?
Use 16 inches OC for most straight layouts. Use 12 inches OC for diagonal decking and many composite layouts.
Do I need railing on my deck?
Most codes require guardrails when the walking surface is more than 30 inches above grade. Local rules can be stricter.
How deep do deck footings need to be?
Footings should reach below local frost depth. That can be about 12 inches in warm regions and 36 to 48 inches in colder regions.
Can I reuse old deck framing?
Maybe. Check rot, joist spacing, fasteners, and ledger flashing. Composite resurfacing often needs tighter joist spacing.
What deck size fits a table and grill?
A 12 x 16 deck is a practical starting point. It fits a dining set, grill, and walkway space without feeling tiny.
Deck Material Estimates for Common Projects
Budget-Friendly Starter Deck
12 x 16 ft rectangle | pressure-treated | 3 ft high
A straightforward rectangular deck with stairs and railing. PT 5/4x6 boards at 16" OC keeps waste at 10%.
~$3,350 DIY materials·~$7,200 installed
Mid-Range Composite Entertainer
16 x 20 ft rectangle | composite | 4 ft high
320 sqft with mid-grade composite for a maintenance-free space. The 4-foot height requires railing on all open sides.
~$6,300 DIY materials·~$14,000 installed
Premium L-Shaped Wraparound
20 x 14 ft + 10 x 10 ft L-shape | premium composite
380 sqft L-shaped wraparound with premium capped composite boards. L-shape adds framing complexity and increases waste to 12-15%.
~$9,700 DIY materials·~$20,300 installed
Deck Building Mistakes That Cost You Money
Skipping ledger flashing
Flash the ledger before decking begins. Water trapped behind the ledger can rot the house rim joist.
Shallow footings
Set footings below local frost depth. Shallow posts move when the ground freezes and thaws.
Wrong fasteners
Use exterior structural connectors rated for treated lumber. Interior screws and light hardware are not enough.
No board waste
Add 10% for straight boards and 15% for diagonal layouts. End cuts and bad boards are normal.
Skipping permits
Attached or raised decks often need permits. Unpermitted work can complicate resale and insurance.
Wide joist spacing for composite
Composite often needs 16 inch OC or tighter. Diagonal layouts commonly need 12 inch OC.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.