Deck Screw Calculator
Count the screws for deck boards that run across the joists. Enter the deck size and the board details, and the boards, joists and screws follow.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Boards are counted across the width of the deck by dividing the width by each board plus its gap. Joists are counted along the length at their spacing, plus one at the far end.
Each board takes the set number of screws, usually two, at every joist it crosses. Multiply the boards by the joists by the screws per crossing to get the total.
Worked example
A deck 12 ft long and 10 ft wide, with boards 5.5 in wide on joists 16 in apart, needs 420 screws.
Questions
How long should the screws be?
Length depends on the board thickness and the joist. Check the screw maker chart for your boards.
Why two screws at each joist?
Two screws hold a board more firmly than one. Many builders use two, but check the board maker instructions for yours.
Should I add spares?
A few spares help with cut ends and missed screws, so many people add a small allowance.
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