Deck Calculator
Calculate deck calculator lumber boards joists. Precise material estimations for building contractors and DIY home builders across USA/UK/Canada.
Calculate Deck Calculator
Enter project dimensions below to compute required material quantities.
Calculation Results
Calculated using verified construction formula: Decking Boards = Math.ceil( ( (Length * 12 / 5.5) * Width / 16 ) * (1 + Waste Margin Pct) )
Quick Summary
The Deck Calculator estimates 16-foot decking boards, floor joist framing counts, 4x4/6x6 support posts, 80lb concrete footing bags, joist hangers, ledger board hardware, and total project costs for pressure-treated wood, cedar, and composite decks.
- Complete Deck Package Scoping: Itemizes surface decking boards, 2x8 joist framing lumber, 4x4/6x6 posts, and concrete footings.
- Material Flexibility: Computes cost estimates for pressure-treated pine (/sq ft), cedar (/sq ft), and composite decking (/sq ft).
- Hardware & Footing Breakdown: Calculates joist hangers, ledger board screws, and 80lb concrete bags.
How to Use the Deck Calculator
- Enter Deck Length in feet (along house).
- Enter Deck Width / Projection in feet (extending out).
- Select Decking Material Type (5/4x6 Pressure-Treated standard).
- Adjust the Waste Margin (%) (10% standard).
- Click Calculate to view decking boards, joists, posts, concrete bags, hardware, and total deck estimate.
Deck Calculator Formula & Method
This tool utilizes verified construction geometric formulas to compute material requirements:
Total Linear Feet = Math.ceil( ((Length * 12 / 5.5) * Width) * (1 + Waste Margin / 100) )
16-ft Deck Boards = Math.ceil(Total Linear Feet / 16)
Where:
- 5/4x6 Decking Board: Standard wood decking board measuring 1 inch actual thickness x 5-1/2 inches actual face width.
- Ledger Board: Heavy 2x8 or 2x10 pressure-treated lumber bolted directly to house rim joist to support deck edge.
- Joist Spacing: 16 inches on-center for wood decking; 12 inches on-center for composite decking.
Worked Example
Example: 20ft * 16ft Pressure-Treated Wood Deck (320 sq ft)
- Surface Area: 20 ft * 16 ft = 320 sq ft
- Total Linear Feet: ((20 * 12 / 5.5) * 16) * 1.10 = 768 linear feet
- 16-ft Deck Boards: 768 / 16 = 48 Boards
- Joists Needed: (20 * 12 / 16) + 1 = 16 Joists
Applying the formula yields:
Total Deck Cost Estimate: 320 * = ,040.00
16-Foot Decking Boards: 48 Boards
2x8 Floor Joists (16ft): 16 Joists
Support Posts & Concrete Bags: 6 Posts & 12 Concrete Bags
What This Calculator Includes vs. Does Not Include
What This Calculator Includes
- Complete Deck Framing & Decking System Engineering: Measures decking boards, joists, beams, support posts, concrete footing bags, joist hangers, and total project costs.
- Material Option Multipliers: Computes cost variations for pressure-treated, cedar, and composite decks.
What This Calculator Does Not Include
- Staircase Assembly & Metal Railing Kits: Decorative railing kits.
Tips & Best Practices
- Use 1/8-Inch Spacing for Wet Pressure-Treated Boards: Pressure-treated lumber shrinks as it dries; gap wet boards 1/8 inch so gaps settle to 1/4 inch.
- Flash House Ledger Board with Z-Flashing: Install stainless steel or vinyl Z-flashing over ledger board to prevent rain water from rotting house rim joist.
Common Mistakes to Avoid
- Using 16-Inch Joist Spacing for Diagonal Composite Decking: Composite decking laid at a 45-degree angle requires joists spaced 12 inches on-center to prevent board sagging.
Frequently Asked Questions (FAQ)
How much does a 20x16 deck cost to build?
A 20x16 foot deck (320 sq ft) costs ,000 to ,000 in pressure-treated wood (,000 to ,000 in composite decking).
How many 16-foot 5/4x6 deck boards for a 20x16 deck?
A 20x16 foot deck requires 48 16-foot 5/4x6 decking boards (768 linear feet).
How many joists do I need for a 20-foot deck?
A 20-foot deck with joists spaced 16 inches on-center requires 16 floor joists.
What size joists are needed for a 16-foot span deck?
A 16-foot joist span requires 2x10 or 2x12 pressure-treated southern yellow pine joists.
How deep should deck post footings be?
Deck post footings must extend below the local frost line (typically 36 to 48 inches deep).
How many bags of concrete per deck post?
Plan on 2 80lb bags of concrete mix per 12-inch diameter post footing hole.
What screws are best for pressure-treated decks?
Use 3-inch polymer-coated deck screws or 305 stainless steel screws.
How many support posts for a 20x16 deck?
A 20x16 deck supported by a doubled 2x10 beam requires 6 4x4 or 6x6 support posts.
Is this deck calculator free to use?
Yes, TibCal's Deck Calculator is 100% free.