Published on · 2 min read
How to plan a container load: cubing, CoG, VGM and weight limits
Dividing volumes is not cubing: planning a load takes real geometry, centre of gravity (CTU Code), SOLAS VGM and the legal road weight — which is not the container’s max gross.
A 40-foot high cube offers 76 m³ and a payload above 28 tonnes. On paper almost anything fits; at the ramp, it doesn’t. Planning a load is a geometry problem, a stability problem and a compliance problem at once — and any of the three can sink the plan of the other two.
Cubing is not dividing volumes
The “container volume ÷ box volume” shortcut systematically overestimates: it ignores feasible orientations, the gaps each row leaves and stacking constraints. The real problem (3D container loading) is NP-hard: no fast method guarantees the optimum, and any serious tool works with heuristics that produce a good, reproducible plan — not the best possible one.
Centre of gravity: the CTU Code 60/40 rule
The CTU Code (IMO/ILO/UNECE) recommends keeping the cargo’s centre of gravity within ±5% of the container’s mid-length — the so-called 60/40 rule — and as low as possible. An off-centre CoG overloads one end, complicates crane handling and can make the truck’s axle split unworkable.
VGM: mandatory before shipment
Since 2016, SOLAS (regulation VI/2) requires the verified gross mass (VGM) of every container to be declared before it is loaded on board. There are two methods: weigh the packed container (Method 1) or sum the declared cargo weights plus the tare (Method 2). No VGM, no loading.
Max gross is not the legal road weight
A 40-foot container structurally accepts over 32 gross tonnes, but to move it by road you must subtract the tractor and chassis tare (roughly 13.5 t nominal) from the national limit. Spain allows 44 tonnes for national transport since October 2025 (Order PJC/780/2025); international traffic remains under Directive 96/53/EC: 40 tonnes (44 intermodal). A container packed to its structural limit can be illegal to haul.
Mistakes that keep happening
- Cubing by dividing volumes and discovering at the ramp that two pallets don’t fit.
- Concentrating weight at one end: CoG outside the 60/40 rule and an overloaded drive axle.
- Confusing the container payload with what can legally be moved by road.
- Stacking without checking the maximum weight the cargo underneath can bear.
To test a load plan with all of these checks — 3D view, CoG, VGM and country limits — you can use this site’s load planner: everything runs in the browser and nothing is stored.