It seems that you need to allow plenty of extra LECA, because an extra 5-6 cubic metres (12-15%) went into the base than we were anticipating. Our internal ground floor area is 95sqm, with the LECA laid to 365mm deep. That equates to 36 cubic metres, so allowing for compaction etc we expected to use 39 cubic metre bags as ordered. We actually ended up using 44.5 cubic metre bags. Luckily we had ordered extra to fill the cavity which we could use instead. We will now need to re-order more for the cavity.