Screw Calculator
Work out how many screws you need for decking, siding or other building projects, based on area and consumption per square meter.
How to use the screw calculator
- Enter the area to be screwed down — for example decking or siding.
- Enter how many screws are needed per square meter for your project.
- Enter a waste percentage to account for misfires and spares.
How screw consumption is calculated
The calculator multiplies the area by the screw consumption per square meter, and adds waste:
Deck boards are normally screwed down with 2 screws per board at each joist they cross — work out the number of joists and boards for a more exact figure, or use a general estimate like 12–16 screws per m² for standard joist spacing.
Frequently asked questions
What screw length should I use for deck boards?
A common rule of thumb is that the screw should go at least 2–2.5 times the material thickness into the joist below. For 28 mm deck boards, that often means 50–60 mm screws.
Should I pre-drill before screwing?
Yes, especially near board ends, to avoid splitting the wood. Many decking screws have a self-drilling tip that reduces the need somewhat, but pre-drilling always gives a neater result.