Decking Calculator
Find out how many deck boards, screws and joists you need for a deck.
| Item | Amount |
|---|---|
| Board length in total | |
| Deck screws | |
| Joists | |
| Estimated board cost |
Shopping list
How the decking calculator works
Each board row covers the board width plus one gap. The calculator divides your deck area by that to get the linear feet of board needed, adds your extra percentage for cuts and waste, then divides by the board length and rounds up.
- Screws: two per board at every joist it crosses, plus a small allowance.
- Joists: the number needed across the deck length at your spacing, each as long as the deck width.
Worked example: a 16 ft x 12 ft deck with 6 in boards
The deck is 192 sq ft. With 5.5 in boards and a 1/8 in gap, each board row covers 5.625 in, so you need about 410 linear feet of board. Adding 10% brings it to about 451 linear feet, which is 38 boards of 12 ft. At 16 in joist spacing you need about 676 screws and 13 joists of 12 ft.
Typical extra to order
| Layout | Extra |
|---|---|
| Straight, 90 degrees to joists | 10% |
| Diagonal, 45 degrees | 15% |
| Chevron, herringbone or inlays | up to 20% |
Frequently asked questions
How many deck boards do I need?
Divide the deck area by the area one linear foot of board covers including the gap, add 10 to 20 percent depending on the layout, divide by your board length and round up.
How big should the gap between boards be?
About 3/16 to 1/4 inch for composite with hidden fasteners. Some installers leave about 1/8 inch for pressure-treated wood, and very wet boards may be installed tight so they gap as they dry. Follow your board maker's instructions.
How many screws do I need for a deck?
Two screws go in each board at every joist it crosses. With joists 16 inches apart, that is roughly 350 screws per 100 square feet for 6 inch boards. Use screws long enough to sink about 1-1/2 inches into the joist.
What is not included?
The joist count assumes a simple rectangle with joists running out from the house. Rim joists, beams, posts, footings, railings and hardware are not included, and local building codes may add requirements.
Estimates only. Board sizes, joist spans and spacing depend on your product and local code.