Think in groups, not room counts
Room-count estimates vary too much to be precise. Group belongings into large furniture, appliances, boxed contents and awkward items, then discuss that list with the storage team.
Packing changes the usable capacity
Removing table legs, standing mattresses safely and using consistently sized boxes can reduce wasted gaps. Heavy boxes belong at the bottom; soft or fragile items should not carry weight.
Leave space for the items you need
A tightly filled unit uses more capacity but makes retrieval difficult. If stock, files or seasonal equipment will be collected regularly, plan clear zones and an aisle from the door.