Deck Calculator
Calculate decking boards, linear feet, and full costs for wood or composite decks. Accounts for board gaps, waste, and any deck shape.
Area Shape *
Rectangle — Length × Width
Frequently Asked Questions
How to Calculate Deck Boards and Material Needed
Building a deck is one of the best investments you can make in your home — it adds outdoor living space and increases resale value. But accurately calculating how many boards you need, and what it will cost, is essential before you visit the lumber yard or order composite panels. Our free deck calculator handles all the math, including board gaps and waste from cuts.
The formula for deck boards is: Boards = Total Area ÷ (Board Length × (Board Width + Gap)). For example, a 200 sq ft deck using 12 ft boards that are 5.5 inches wide with a 0.25 inch gap: effective board width = 5.75 inches = 0.479 ft. Board area = 12 × 0.479 = 5.75 sq ft. With 15% waste: 200 × 1.15 ÷ 5.75 = 40 boards. Our calculator does this instantly.
Deck Material Comparison — Wood vs Composite
| Material | Cost / Sq Ft | Lifespan | Maintenance |
|---|---|---|---|
| Pressure Treated Wood | $2–$5 | 15–25 yrs | Stain every 2–3 yrs |
| Cedar | $5–$8 | 15–20 yrs | Seal every 1–2 yrs |
| Composite (Trex) | $8–$15 | 25–30 yrs | Minimal — wash only |
| Ipé Hardwood | $15–$25 | 40–75 yrs | Oil yearly |
| PVC | $10–$18 | 30+ yrs | Virtually none |
Board Sizing — Nominal vs Actual Dimensions
One of the most common mistakes when calculating deck boards is using the nominal (labeled) size instead of the actual size. A 2×6 board is labeled as 6 inches wide but the actual width after milling is 5.5 inches. A 5/4×6 deck board is actually 5.25 inches wide. Always use actual dimensions in our deck board calculator — our dropdown options show both nominal and actual sizes so you never make this mistake.
Pro Tips for Deck Building
- ▸Use hidden fasteners for composite — they give a clean surface look and are required by most composite manufacturers to maintain warranty.
- ▸Let pressure treated wood dry — new PT lumber contains moisture. Wait 6 months before staining or sealing, otherwise the finish will peel.
- ▸Add 15–20% for diagonal patterns — diagonal or herringbone deck layouts create more cut-off waste. Increase your waste percentage accordingly in the calculator.
- ▸Pre-drill Ipé and hardwood — exotic hardwoods are extremely dense and will split without pre-drilled pilot holes at every fastener point.
- ▸Use stainless or hot-dipped galvanized fasteners — regular zinc screws corrode quickly outdoors, especially near coastal areas or with pressure treated lumber.
Use our free deck calculator above for any deck shape and material type. Enter your board dimensions and gap spacing to get exact board count, linear feet, and a full material plus labor cost estimate — no sign-up required.