DeckMath
400 sqft · 20 × 20 ft

20×20 Deck Cost

A 20×20 square deck (400 sqft) is a favorite for outdoor kitchens + dining + lounge — the smallest size where 3 zones comfortably coexist. The calculator below is pre-loaded with these dimensions — change the state, finish tier, or scope to recalculate live.

400 sqft80 ft perimeter5 finish tiersAll 50 states2026-Q1 pricing
20×20·Footprint
400·Sq ft
80·Perimeter ft
<2s·Live calc

What a 20×20 deck costs by finish tier

Tier$/sqft (installed)Total range
Budget · Pressure-treated$25–$40$10,000–$16,000
Mid · Cedar / premium PT$35–$55$14,000–$22,000
Premium · Mid composite$50–$80$20,000–$32,000
Luxury · Premium composite$75–$110$30,000–$44,000
Exotic · Tropical hardwood$90–$140$36,000–$56,000

National-average pricing 2026-Q1. Northeast +22%, West Coast +28%, South -8%, Midwest baseline. Use the calculator below for precise state + scope adjustments.

Inputs

Dimensions

Plan-view length × width.

ft

ft

Area · 400 sq ft·Perimeter · 80 ft
in

IRC R312 requires a 36″ guardrail above 30″.

400 sq ft deck. Mid composite tier. Project total $30,802 to $54,153, 77 to 135 dollars per square foot.
Project budget · Northeast
$30,802 – $54,153$77–$135 /sq ft

400 sq ft · Mid composite · 1.22× labor · 1.10× complexity

Materials
Low $9,900
Labor
Low $14,762
Add-ons
Low $5,666
Soft costs
Permit · demo · design

Project advisories · IRC 2021

Guardrail included (deck 36″ off grade)

IRC R312

IRC R312 mandates a 36″ guardrail on open edges when deck height exceeds 30″. 60 lf priced at Mid composite tier.

Building permit included in budget

IRC R105

Northeast typical permit fee is in the budget. Most jurisdictions require a permit for decks > 200 sqft, > 30″ above grade, or attached to the house.

Hidden-fastener install premium baked in

Manufacturer specs

Mid composite uses hidden-fastener clip systems (Cortex / CamoClip / Trex Universal) — labor takes 25–30% longer than face-screwing PT. Already inside the tier's installed $/sqft band.

Cost breakdown

Labor (Northeast, 1.22× national)
$14,762 – $23,619 (low – high estimate)
1.0 scope
$23,619
Materials (decking + framing + hardware)
$9,900 – $15,840 (low – high estimate)
Home DepotLowe’s
1.0 scope
$15,840
Railing (60 lf, ledger 3-side)
$4,026 – $6,954 (low – high estimate)
1.0 scope
$6,954
Contingency (10% reserve)
$0 – $4,923 (low – high estimate)
1.0 scope
$4,923
Stairs (4 steps @ 9.0″ rise)
$1,640 – $2,342 (low – high estimate)
1.0 scope
$2,342
Building permit (Northeast)
$474 flat
1.0 scope
$474
Materials subtotal
$54,152

National-median pricing (2026-Q1). Local prices vary ±15%. Materials line uses Mid composite tier; switch tiers to repaint the budget. Includes 10% contingency reserve on the high estimate.

Live preview

Visualize your deck

Photoreal 3D · plan view · framing breakdown. Color matches your tier selection.

PBR materialsHDR lightingMid composite
Loading 3D scene…
20′ × 20′
Trex Enhance
Joists
16 × 20′
Beams
2 × 2-ply 2×10
Posts
8 × 6×6
Boards
44 rows

Project all-in

Materials (low – high)
Mid composite tier · Trex Enhance · Fiberon Good Life · TimberTech Prime+. ~$0.05/sqft/yr.
$9,900 – $15,840
Labor (installed)
Northeast · 1.22× national index
$14,762 – $23,619
Add-ons
Railing · stairs · lighting (only included items)
$5,666 – $9,296
Soft costs
Permit · demo · design (only included items)
$474 – $474
Contingency reserve (10%)
Industry-standard cushion for unforeseen scope
$4,923
Project total (low – high)
Plan around the high. Get 3 contractor bids — DeckMath should land within ±15%.
$30,802 – $54,153

Same dimensions, different tier

tap to switch

DIY savings

$25,813
vs mid-range contractor
  • Materials only: $15,840
  • Estimated hours: 600 hr
  • Skill required: advanced

Finance estimate

$1,124/month
60-month personal loan @ 8.99% APR
  • Principal: $54,153
  • Total interest: $13,279
  • Estimate only — shop 3+ lenders.
Composite/PVC installs use hidden-fastener clip systems — labor is 25–30% slower than face-screwing pressure-treated wood. That premium is already baked into the tier's installed $/sqft band.

Need exact board counts?

The Deck Material Calculator gives you a permit-ready bill of materials — every joist, hanger, fastener, and footing — validated against IRC 2021 span tables.

Open

Estimates use 2026-Q1 national-median pricing (Home Advisor, Angi, RSMeans). Expect ±15% variance vs your local market. Always get 3 contractor bids before signing. This calculator is not a substitute for a licensed inspector or structural engineer.

FAQ — 20×20 deck

How much does a 20×20 deck cost?

A 20×20 deck (400 sqft) costs $10,000-$16,000 for budget pressure-treated construction, $20,000-$32,000 for mid-range composite, and $36,000-$56,000 for premium composite or tropical hardwood. National-average pricing — multiply by 0.92× for the South or 1.28× for West Coast labor.

How many boards do I need for a 20×20 deck?

Running 5/4×6 or 1×6 deck boards (5.5″ face, 1/8″ install gap) parallel to the long dimension: rows = ceil(20 × 12 ÷ 5.625) = 43 rows. Total LF = 43 × 20 × 1.07 (7% waste, parallel pattern) ≈ 921 LF. Round up to 20-ft stock for typical 47 boards.

How long does it take to build a 20×20 deck?

For a contractor crew (2-3 people), a 20×20 deck takes 4-7 days depending on complexity, including framing + decking + railing + inspection wait. DIY single-person build: 60-75 weekend days for composite, less for pressure-treated.

Do I need a permit for a 20×20 deck?

In most US jurisdictions, yes. IRC 2021 R105 requires a permit for any deck above 30″ off grade, attached to the house, or larger than 200 sqft. A 20×20 deck (400 sqft) exceeds the 200-sqft threshold and definitely requires a permit.

Other popular deck sizes

10×8
80 sqft
10×10
100 sqft
12×10
120 sqft
12×12
144 sqft
14×12
168 sqft
16×12
192 sqft
20×12
240 sqft
16×14
224 sqft
See all 20 deck sizes →