The packaging limit is only part of the decision
Read the information printed on the box first. Its stated capacity assumes the intended assembly and an undamaged condition. Softened bottoms, torn handles or repeatedly repaired seams do not automatically retain that capacity. Use a suitable, intact box for dense contents.
The load rating also says nothing about whether you can comfortably carry the box through a narrow stairwell. A large container may be awkward because of its dimensions alone. Choose small formats for dense items and distribute the contents between several containers early in the process.
Pause as you fill each box
Keep scales nearby if you are packing several similar boxes. Comparing their weights helps identify unusually heavy ones. The number supports your judgement; it replaces neither manufacturer instructions nor assessment of the route. Mark the actual weight clearly on any unusually heavy container.
Carefully check whether you can handle the box in a controlled way without forcing a sudden movement. If unsure, divide the contents. A brief check at floor level does not mean a longer journey or a flight of stairs will be equally manageable.
Fill spare space with light material
A half-full box of books may already have its complete load. Secure the remaining space with light, clean cushioning so the books cannot topple. Do not add heavy objects simply because there is room above them. The lid should close without bulging.
Make it clear which boxes need particular attention when handing them over. A readable label helps other people, but does not make an overloaded box lighter. Repack troublesome containers before moving day, while spare packaging is still readily available.
