Deck Calculator
To estimate deck materials, multiply length × width for the deck area, then divide by each board's coverage (width × length) to get the board count — add 5% for waste. Add joists at 16 inches on center and about 350 screws per 100 sq ft. A 16×12 ft deck (192 sq ft) needs roughly 45 boards, 13 joists, and 670 screws.
- Joist spacing
- 16 in OC
- Board gap
- ~¼ in
- Screws
- ~350 per 100 ft²
Your measurements
Actual width — 5.5 in for a nominal 6-inch board.
Enter your measurements
Fill in the fields to see your estimate.
The formula
Deck area = Length × Width; Boards = (Width ÷ board width) × (Length ÷ board length) × wasteHow to calculate it manually
- 1
Measure the deck
Multiply length × width for the total surface area.
- 2
Pick a board size
Most deck boards are 5.5 in wide (nominal 6 in) in 8–20 ft lengths.
- 3
Count boards & joists
Divide by board coverage for boards; space joists 16 in on center.
- 4
Add fasteners & waste
About 350 screws per 100 sq ft, plus 5–10% waste for cuts.
Example calculation
A 16 ft × 12 ft deck = 192 ft². With 5.5-in × 12-ft boards: ~27 rows × 2 = ~54 boards after waste; joists 16/12 ≈ 13; screws ~670.
Deck cost by material
Installed cost per square foot, including framing and labor.
| Decking | Cost per ft² (installed) | Lifespan | Notes |
|---|---|---|---|
| Pressure-treated wood | $15 – $25 | 10–15 yrs | Cheapest, needs sealing |
| Cedar / redwood | $20 – $35 | 15–20 yrs | Natural look |
| Composite | $25 – $45 | 25–30 yrs | Low maintenance |
| PVC / capped | $30 – $60 | 30+ yrs | Most durable |
Common deck estimating mistakes
Forgetting the framing
Joists, beams, posts, and footings aren't in the board count — they're a big part of the material list and cost.
Ignoring board gaps
Deck boards need a ~¼-inch gap for drainage and expansion, which affects how many boards fit.
Under-ordering fasteners
Face-screwed decks use ~350 screws per 100 sq ft; hidden fasteners have their own counts.
Skipping permits and footings
Most decks need a permit and proper footings below the frost line — plan for both.
Frequently asked questions
Related guides
Related calculators
Ready to start your decking project?
Run the numbers above, then explore related tools and guides to plan every step.