Crunch Deck Material Estimator
Enter your deck's length and width to estimate deck boards, joists, screws, and concrete footings — a solid shopping list before you head to the lumber yard.
| Deck area | 0 sq ft |
| Joists (16″ on center) | 0 |
| Deck screws | 0 |
| Concrete footings | 0 |
| 80-lb concrete bags | 0 |
How it works
Assumptions: 5.5″-wide deck boards with a ⅛″ gap (5.625″ effective width), boards laid across the deck width. Board count = length ÷ 5.625″, rounded up. Joists run 16″ on center along the length. Screws: 2 per board per joist. Footings: roughly one per 50 sq ft, with two 80-lb concrete bags each.
Formula & worked example
Formula: Boards = deck length in inches ÷ 5.625 in (a 5.5-in board plus its gap), rounded up. Joists = floor(deck length in inches ÷ 16) + 1, for 16-in spacing; screws = boards × joists × 2. Footings = deck area ÷ 50 sq ft, rounded up, with 2 bags of concrete per footing.
Worked example: A 16 ft × 12 ft deck covers 192 sq ft: 192 ÷ 5.625 rounds up to 35 boards, with 13 joists, about 910 screws, 4 footings and 8 bags of concrete.
Frequently asked questions
How many deck boards do I need?
Divide the deck length (in inches) by 5.625 (a 5.5″ board plus a ⅛″ gap) and round up. A 16-ft-long deck needs about 35 boards.
How many screws per deck board?
Two screws at every joist crossing. For 16″-on-center joists, a 12-ft board needs about 20 screws.
How deep should deck footings be?
Footings must extend below your local frost line — commonly 36″ deep in cold climates. Always check local building code and permits first.
🛠️ More project math
Figure out paint for the railing with the paint coverage calculator, or compare lumber prices per board foot.