Measure the bounding space
Record the maximum length, width and height with units and orientation. Add a sketch or photos so the packaging supplier can distinguish empty corners from projecting parts.
Mark permitted support areas
Identify surfaces that can carry the item and those that cannot. Include the actual weight and any orientation restrictions. Keep unknowns in the brief rather than making the shape look simpler than it is.
Review the assembled system
Discuss proposed blocking, internal support and the base with the supplier. The outside carton should be assessed as one part of that system. Confirm final dimensions after the design is settled.
Technical context: FedEx · freight packing guidance ↗. This note prepares a specification conversation. Confirm the actual design and shipping requirements with the responsible supplier and carrier.