Export loading starts with the folded footprint, not the open cage: measure length, width and the stacked thickness of each folded unit before quoting a container load.
The method is simple: internal length x width x height of the container, divided by the folded unit volume, then reserve 8-12% for packing clearance and securing. Leave working space near the doors as well.
Take a common 1200x1000 folding cage: folded thickness is roughly 0.15-0.2 m and units nest in a stack. A 20GP measures about 5.9x2.35x2.39 m internally and a 40HQ about 12.03x2.35x2.69 m, so the estimate follows the formula, with the measured folded thickness as the final input.
Two points are often missed: uneven stacks leave gaps that reduce real capacity, and timber, straps and rust film also take space. Ask the maker to verify the loading plan against the actual packing method.
Nanjing Tongnuo (Xintongnuo) provides measured folded thickness and loading estimates for export orders, with rust-preventive packing and securing; call +86-25-84935609 or +86-18061678988.