The internal and external dimensions of a warehouse cage differ a good deal. Many purchasers order by external dimensions only and then find the goods won't fit—the most common sizing pitfall. Internal dimensions are the usable space inside the cage, while external dimensions are the overall footprint including mesh and frame.
How big is the difference? Typically, on each side you subtract the wire diameter plus the frame width plus the post outer diameter—about 20 to 40mm per side. A standard cage with external dimensions of 1200×1000mm often has internal dimensions of only about 1140×940mm, so parts must be measured against the internal dimensions before loading.
What do external dimensions determine? The cage's footprint, stacking arrangement, pallet fit and truck loading. What do internal dimensions determine? How large a part can fit, how many parts fit, and whether dividers are needed. Both dimensions serve different purposes and both must be given to the manufacturer when selecting.
What confuses people is the folded-state dimensions. When folded, the cage's height drops sharply, but its length and width stay at the external dimensions, because the mesh and posts do not narrow when folded. Empty cages shipped back are volume-calculated by folded height, yet arranged on the floor by external footprint.
Practical tip: first measure the length, width and height of your largest part, then leave a 20 to 30mm margin when choosing internal dimensions; work back from pallet or truck fit to set external dimensions. Nanjing Tongnuo supports non-standard internal-dimension customization; always provide the maximum outer dimensions of your parts before ordering.