Wood Screw Quantity Calculator
Screws are sold by the box and weight, not the piece, so you need a number that survives the round trip to the hardware store. This counts structural fasteners at standard spacing and converts to boxes.
Results
Enter your measurements above and press Calculate.
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How this is calculated
- Boards = area / (5.5 / 12), using the real face width of a 1x6 rather than the nominal 6 inches
- Decking screws = boards x 2, one at each joist crossing
- Framing screws = (area / joist spacing) x screws per joist, at one screw every 6 inches along each joist
- Total = (decking + framing) x (1 + waste percentage), rounded up
Two per board is a floor, not a target: wide boards, stair treads and any board crossing three or more joists usually want two screws at every crossing rather than two per board. Using 5.5 inches instead of 6 matters more than it looks, because the nominal figure understates how many boards a given area needs by about 8 percent. The waste allowance covers dropped screws, stripped heads and the ones that go in at a bad angle: 10 percent is normal for a deck, 15 percent for a first project in a tight space.
Questions people ask
How many screws for decking?
Two screws per board at each joist crossing is the structural minimum. For a 16×20 deck with 1×6 decking at 16 inch joist spacing, that works out to roughly 300 structural screws plus the framing and railing connections.
What size screws for decking?
2½ to 3 inch structural screws rated for pressure treated lumber. Ordinary drywall screws have a weak head that strips in treated wood. Use screws specifically labeled for exterior or ground contact.
Do galvanized screws rust in pressure treated lumber?
Modern ACQ treated lumber is far less corrosive than the old CCA era, and standard hot-dip galvanized screws perform acceptably. In coastal or wet conditions use stainless or manufacturer-coated structural screws.
Screws or nails for framing?
Screws have three to ten times the withdrawal strength of nails, which matters on decks and any structure that may flex. Many inspectors now require screws for decks and outdoor framing. Nails remain fine for interior wall plates.
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