Decking Calculator
Calculate exactly how many deck boards, joists, screws, and footings you need. Supports standard wood and composite decking.
How to Calculate Deck Materials
Building a deck starts with knowing your dimensions. Multiply the length by the width to get total square footage. From there, you can calculate the number of deck boards based on board width and length, joists based on spacing, and support posts and footings based on your deck's layout. Always add 10–15% extra for waste, cuts, and mistakes.
Decking Material Comparison
| Material | Cost per Sq Ft | Lifespan | Maintenance |
|---|---|---|---|
| Pressure-Treated Pine | $2–$5 | 10–15 years | Stain/seal every 2–3 years |
| Cedar | $4–$8 | 15–20 years | Seal every 2–3 years |
| Composite | $8–$15 | 25–50 years | Virtually none (wash only) |
Joist Spacing Guide
Joist spacing determines how sturdy your deck feels underfoot. The standard is 16 inches on center, which works well for most decking materials. Use 12-inch spacing for diagonal decking patterns, composite boards, or areas with heavy loads like hot tubs. 24-inch spacing is only suitable for thick, strong boards in low-traffic areas.
Footing and Post Requirements
Every deck needs concrete footings to support the weight. Footings should extend below the frost line in your area (typically 36–48 inches deep in cold climates). Posts are typically spaced 6–8 feet apart, and each post sits on its own concrete footing. Check your local building codes for specific depth and size requirements.
Tips for Your Deck Project
- Check if you need a building permit — most decks over 200 sq ft or 30 inches high require one.
- Use galvanized or stainless steel screws and hardware to prevent rust and staining.
- Leave a 1/8-inch gap between deck boards for drainage and expansion (1/4 inch for composite).
- Always attach your deck to the house with a properly flashed ledger board to prevent water damage.
- Pre-drill screw holes near board ends to prevent splitting, especially with hardwoods.
- Call 811 before digging footings to have underground utilities marked for free.
Frequently Asked Questions
DIY deck costs range from $8-$15 per square foot for pressure-treated wood, $15-$25 for cedar, and $25-$45 for composite decking. These include framing, decking boards, and hardware. Professional installation adds $15-$35 per square foot for labor. A typical 12x16 deck (192 sq ft) costs $1,500-$3,000 in materials for a DIY build.
For a 12x16 foot deck using standard 5.5-inch wide boards (2x6) running the 16-foot length, you need approximately 26-28 boards with 10% waste included. The exact number depends on your board width and the gap spacing between boards (typically 1/8 inch for wood or 1/4 inch for composite).
Pressure-treated wood is the most affordable and widely available, lasting 10-15 years with regular maintenance. Cedar offers natural beauty and rot resistance for 15-20 years. Composite decking costs more upfront but lasts 25-50 years with virtually no maintenance — no staining, sealing, or sanding required. Choose based on your budget and willingness to maintain.
Most jurisdictions require a building permit for decks over 200 square feet, higher than 30 inches off the ground, or attached to the house. Even small ground-level decks may require permits in some areas. Permits ensure your deck meets structural and safety codes. Check with your local building department before starting construction.
Standard deck joist spacing is 16 inches on center, which works well for most wood and composite decking. Use 12-inch spacing for diagonal board patterns, thinner deck boards, or areas supporting heavy loads like hot tubs. 24-inch spacing is only suitable for thick, strong boards on low-traffic decks.