Balusters make one more gap than there are balusters, and the two against the posts count. That is where DIY railings fail inspection — people space them evenly across the middle and forget the ends.
Enter the clear span, the baluster width and your maximum gap. We'll work out the count and spread every gap evenly — including the two nobody counts.
Works in metric and US imperial — you choose at the start and can switch at any time. Every figure this calculator uses is published with its source, and the result comes with a printable order sheet. No account, no email, and nothing you type leaves your browser.
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And the two against the posts count. That is where DIY railings fail inspection: people space the balusters evenly across the middle and forget the space at each end, which is usually the widest gap in the whole run. A 2,000 mm clear span with 32 mm balusters and a 100 mm limit needs 15 balusters — giving 16 gaps of 95 mm each, all of them legal.
100 mm and 4 in are the common limits, but they are not universal. Pool barriers are tighter, and some jurisdictions set different figures for stairs than for landings. It is a five-minute check and it is the difference between a balustrade that passes and one that gets rebuilt. Set out from the centre too — working from one end pushes every accumulated error into the final gap, which is the one an inspector reaches for first.
It is a spacing tool, not a structural check. A balustrade has to resist a sideways load from someone falling against it, and fixings and post sizes come from a code rather than from a gap calculation. Two other things worth knowing: horizontal rails are a climbing aid, and many codes restrict or ban horizontal infill on balconies for exactly that reason — vertical balusters are the safe default. And order two or three spare, because balusters split at the fixing more often than any other small timber component.
Remember that the number of gaps is one more than the number of balusters, because the spaces against the posts at each end count too. Work out the count so that every gap including the end ones falls under the limit, and set out from the centre.
100 mm or 4 in are the common limits, based on a small child's head not passing through. Pool barriers are tighter and some jurisdictions differ between stairs and landings, so check your local figure before cutting anything.
Most often because of the end gaps. People space the balusters evenly across the middle and forget the space between the last baluster and the post, which then turns out to be the widest gap in the run.
Often not. Horizontal infill is a climbing aid, and many codes restrict or ban it on balconies for that reason. Vertical balusters are the safe default.