About Decking Calculation
A decking calculator helps estimate the number of decking boards and total material cost for a deck area. It considers the deck dimensions, board size, spacing, and price to give accurate results before construction.
Formula Used
Number of Boards = Deck Area / (Board Coverage Area)
where Board Coverage Area = (Board Width + Spacing) × Board Length
Example
Deck = 20 ft × 12 ft = 240 ft²
Board = 6" width (0.5 ft) + 0.25" spacing (0.02 ft) = 0.52 ft coverage
→ 240 ÷ (0.52 × 8) = 58 boards required
Deck Board Sizes (Common)
- 5/4 × 6 in (actual 1 × 5.5 in)
- 2 × 6 in (actual 1.5 × 5.5 in)
- Composite boards: 5.5" × 12 ft, 16 ft, or 20 ft
Material Types & Considerations
Pressure-Treated Wood
- Most affordable option
- Requires regular sealing/maintenance
- May shrink or warp initially
- Add 5-10% extra for cutting waste
Composite Decking
- Low maintenance, long-lasting
- Higher initial cost
- Minimal expansion/contraction
- Add 3-7% extra for cutting
Deck Layout Patterns
Straight Run
Most efficient use of materials, minimal waste
Diagonal
Adds visual interest, increases material needs by 15-20%
Herringbone
Premium look, increases material needs by 25-30%
Waste Factor Guidelines
| Deck Complexity | Recommended Waste Factor | Notes |
|---|---|---|
| Simple Rectangle | 5-7% | Minimal cutting, straight runs |
| Multiple Angles | 10-12% | L-shaped or U-shaped decks |
| Complex Pattern | 15-20% | Diagonal or herringbone layouts |
Additional Materials to Consider
Structural Components
- Ledger boards (attached to house)
- Beams and joists
- Posts and footings
- Hardware (joist hangers, screws)
Finishing Materials
- Railing systems and balusters
- Stair treads and risers
- Fascia and trim boards
- Deck lighting
Seasonal Considerations
- Wood Expansion: Allow for 1/8" to 1/4" gaps between boards depending on climate
- Wet vs Dry Lumber: Pressure-treated wood shrinks as it dries - account for this in spacing
- Temperature Effects: Composite materials expand/contract with temperature changes
- Installation Timing: Consider weather conditions for optimal installation
Tips for Accurate Estimation
- Always include 5–10% extra boards for cutting and wastage
- Consider the deck layout and direction of boards
- Account for gaps between boards due to expansion
- Check board availability in local lengths to minimize waste
- Measure twice, order once - verify all dimensions before purchasing
- Consider buying extra matching material for future repairs
- Factor in delivery costs and timing for large orders
- Check local building codes for railing and spacing requirements
Cost-Saving Strategies
- Optimal Board Lengths: Choose lengths that minimize cutting waste
- Bundle Purchases: Many suppliers offer discounts for full bundles
- Off-Season Buying: Purchase materials during winter for better prices
- Local Suppliers: Compare prices from multiple local lumber yards
- Remnant Sales: Check for discounted partial bundles or overstock