Offcut WorksDecking calculators
Everything you need to plan and order a deck, in metres and millimetres. Work through them in order, or jump to the one you need.
- Decking calculator
Boards, joists and fixings for a straight-laid deck, with a plan view and a copyable list.
- Decking board gap calculator
Find the gap that lets whole boards fill the width, so you avoid a thin ripped board.
- Diagonal decking calculator
Boards, cuts, joists and fixings for boards laid at 45 degrees.
- Decking clips and screws calculator
How many hidden clips and screws you need, for your board width and joist spacing.
- Decking subframe calculator
Joists, rim joists, noggins, bearers and posts for the frame under your deck.
- Deck steps calculator
Number of steps, riser height, tread depth and stringers for garden steps.
- Decking cost calculator
Add up boards, frame, labour, steps and handrail using your own prices.
- Decking planning permission checker
Answer a few questions to see whether your deck is likely to be permitted development in England.
Planning a deck: the order to work in
- Check the rules. Start with the planning permission checker. Height, garden coverage and where the deck sits decide whether you need permission, and raised decks may also need building regulations approval.
- Measure and choose boards. Decide on a board width and a gap. The board gap calculator shows how to avoid a thin ripped board.
- Work out quantities. Use the decking calculator for straight boards or the diagonal decking calculator for 45 degree boards.
- Plan the frame. The subframe calculator counts joists, bearers and posts. Check spans against span tables.
- Count the fixings. The clips and screws calculator compares hidden clips with face screws.
- Add steps. The steps calculator gives equal risers and the number of stringers.
- Set a budget. The cost calculator adds it up from your own prices.
Why the defaults need checking
Board makers give different advice on joist spacing and gaps. In the guides we checked, joist centres ranged from 250 mm to 400 mm and gaps from about 3 mm to 8 mm. Each calculator shows its sources and says which defaults we could not confirm. The guide for your boards always takes priority.