Estimate garage shelving and storage needed by items.
Garage shelving is limited by shelf length, not by shelf area, because bins sit in a single row front to back. Dividing usable shelf length by bin width gives how many bins fit per tier, and that must be rounded DOWN because a partial bin does not fit. Dividing the bin count by that figure and rounding UP gives the number of tiers, since a partly filled tier is still a tier you have to build.
Bins per tier
floor(usable shelf length / bin width)
Tiers
ceil(bin count / bins per tier)
Footprint
m2 = shelf length x bin depth / 10,000
A bin that only half fits on a shelf does not fit, so capacity rounds down. But 3.2 tiers of bins still needs a fourth tier to hold the remainder, so tier count rounds up.
No. Stacking upward reuses the same floor area, which is the whole point of shelving. The footprint reflects one shelving unit's floor space.