Free NZ balustrade calculator. Even post spacing, baluster count and the real clear gap to mark out. Verify barrier height and gap against F4/AS1.
This calculator sets out a run of balustrade: how many posts, how many balusters, and the real clear gap to mark between them, which is the figure you actually need standing on the deck with a tape. It does the setting out. It does not decide whether a barrier is required, or how high it has to be.
Give it the length of one straight run and the post centres you are working to, and it divides the run into equal bays no wider than that figure, then back-solves the spacing those bays actually land on. A 3.6m run at 1.0m centres is four bays at 900mm, not three at a metre plus a 600mm stub.
That even division is the same solver CostMate's estimating engine uses to set out a balustrade on a deck estimate. Posts are counted including one at each end of the run.
Do each straight separately if the balustrade turns a corner. A corner post is shared between the two legs, so subtract one post per corner if you add the runs together: otherwise you count it twice.
Dividing the clear span by the gap plus a baluster is the obvious method and it over-orders. The calculator instead finds the smallest number of balusters that keeps every gap at or under your limit, then works out what that gap actually is.
Worked through: a 1000mm bay with a 90mm post leaves 910mm of clear span. Six 45mm balusters make seven gaps of 91.4mm. The naive division says seven balusters; six is enough, and the gaps come out even rather than leaving an odd one at the end.
The page gives you both the clear gap and the baluster centres (gap plus one baluster) because which one you mark to depends on how you are setting out.
The 1000mm barrier height and the 100mm maximum gap are the figures carried in CostMate's own deck engine, shown as starting points you can change. The starting values for post centres, post width and baluster width are also CostMate's allowance, change it to suit. They are not this tool telling you what your barrier has to be.
Whether a barrier is required at all is a fall-height question, and the required height and gap sit in F4/AS1 and differ by where the barrier is and what is below it. Bring those from the current document and your plans.
Barrier height, maximum gap and whether a barrier is needed at all are design decisions. Verify them against current F4/AS1 and your plans, and confirm post and baluster sizes with your merchant, before you order or build.