Building a deck is one of the most popular DIY home improvement projects, adding outdoor living space and increasing your home's value. However, accurately estimating materials is crucial — running short mid-project means delays, while over-ordering wastes money. This guide covers how to estimate every material you will need.
Decking Boards
The most visible and expensive component. To calculate decking:
- Calculate total deck area in square feet using our Square Footage Calculator
- Choose board size (most common: 5/4" × 6" composite or 2" × 6" pressure-treated)
- Calculate board feet needed
For standard 6" wide decking: Linear feet needed = (Deck area × 12) ÷ 5.5 (5.5" actual width)
Number of boards = Linear feet ÷ Board length
Add 15% for waste — this accounts for cuts, defects, and staggered joints.
Joists
Joists are the structural members that support the decking: - Standard spacing: 16" on center (12" for composite decking) - Number of joists = (Deck width in inches ÷ Spacing) + 1 - Joist length = Depth of the deck
Example: 16' × 12' deck with 16" spacing = (12 × 12 ÷ 16) + 1 = 10 joists, each 16' long
Posts and Footings
- Posts: Typically every 6-8 feet along each beam
- Concrete footings: One per post, typically 12" diameter × 42" deep
- Use our Concrete Calculator for footing concrete volume
Beams
Beams run perpendicular to joists and sit on posts: - Number of beams depends on deck depth and joist span capacity - For spans up to 8': Single beam at the outer edge - For spans up to 14': Two beams spaced evenly
Railings
Required for decks more than 30" above grade: - Posts: Every 6-8 feet along the perimeter - Top and bottom rails: 2 per section - Balusters: Spaced max 4" apart (code requirement) - Balusters per section = (Section length in inches ÷ 4) - 1
Stairs
Use our Stair Calculator to determine: - Number of steps - Rise and run dimensions - Stringer length - Number of stringers needed (every 16" of stair width)
Fasteners and Hardware
| Item | Quantity Rule |
|---|---|
| Deck screws | 350 per 100 sq ft of decking |
| Joist hangers | 2 per joist |
| Post bases | 1 per post |
| Lag bolts | 2 per post-to-beam connection |
| Hidden fasteners | 175 per 100 sq ft (if using) |
Estimated Material Costs (2026)
| Material | Cost Range |
|---|---|
| Pressure-treated lumber | $1.50-3.00/linear ft |
| Composite decking | $3.00-8.00/linear ft |
| Concrete (bags) | $5-7 per 80-lb bag |
| Deck screws (5 lb box) | $25-40 |
| Joist hangers | $1.50-3.00 each |
For the most accurate estimates, measure your deck dimensions and use our Square Footage Calculator for area and our Concrete Calculator for footings.