Technical Information > CTU Code – Rule 60/50

CTU Code – Rule 60/50

Rule 60/50 represents one of the key recommendations for safe cargo transport in shipping containers and other cargo transport units (CTU). It is part of the Code of Practice for Packing of Cargo Transport Units (CTU Code), which is an international set of rules and recommendations issued by organizations IMO, ILO and UNECE and recognized worldwide. The rule is also known as the “rule of thumb” and provides simple guidance on how to distribute the center of gravity of cargo in a container for maximum safety.

Principle of the rule:

  • 60% of cargo weight must be placed in the middle half (50%) of the container length.
  • The goal is to keep the center of gravity (Center of Gravity, CoG) as close as possible to the geometric center of the container.

Why is this important?

  • Unstable center of gravity leads to risks during handling, transport and storage of containers (risk of tipping, structural damage, cargo loss, etc.).
  • The rule helps prevent the center of gravity from shifting beyond the permitted tolerance of ±5% of the container length, as specified by the CTU Code.

Technical explanation and container construction

ISO container construction

Container elementFunction
Corner postsCarry most of the load during stacking and handling
FloorCargo placement and distribution, designed for point and area loads
BeamsStrengthen the bottom frame of the container, transfer forces to corner posts
Walls and roofProtect cargo, not designed to carry large loads directly

Containers are designed for even weight distribution. ISO standards (e.g. ISO 668, ISO 1496) specify maximum useful load (payload) and limit values for point loads on the floor.

Consequences of incorrect distribution:

  • Floor overload or individual structural elements lead to deformations, cracks or even container destruction.
  • Eccentric loading increases the risk of tipping, especially during handling with spreaders or during loading/unloading at the ramp.

Principle of correct weight distribution

Why 60% in the middle half?

  • The middle part of the container is the most stable – the geometric center is located here and the structure is strongest here.
  • Dynamic forces during transport (braking, acceleration, turning, wave motion) act least destructively if the center of gravity is in the middle.

Graphical distribution scheme

|---------|---------------------|---------|  
0%2      25%                   75%     100%  
Light    60% weight in         Light  
cargo    middle half           cargo
  • Area 25–75% of length is intended for heavy loads.
  • Both end quarters (at the doors and at the front wall) are intended for lighter cargo, fillers or balancing material.

Physical and safety arguments

Risks of shifted center of gravity

  • Exceeding permitted eccentricity (±5% of length) means:
    • Uncertain lifting of the container with spreader – risk of dangerous tilting.
    • Uneven weight distribution on the floor – possibility of breakthrough.
    • During road transport, increased load on one axle, reduced stability, longer braking distance.
    • On ship, risk of container stack shift, loss of entire blocks at sea.

Practical examples:

  • Incidents: In 2020, according to the World Shipping Council, over 3,000 containers were lost due to stack tipping. A common cause was poor center of gravity distribution and improper packing.
  • Case studies (see Container Handbook): In several cases, containers tipped during terminal handling when the center of gravity was off-center by more than 10% of the length.

Methodology of correct loading according to CTU Code

Step by step:

  1. Planning
    • Determine the exact weight of all pieces, pallets or machines.
    • Create a distribution plan (layout) – ideally digitally or on paper.
  2. Placement of heavy pieces
    • Always start from the center – area 25–75% of length.
    • If the shape of the cargo allows, divide heavy pieces symmetrically.
  3. Lighter cargo and fillers
    • Place at the head and at the doors.
    • Fill gaps against movement (wooden beams, airbags, polystyrene blocks).
  4. Center of gravity check
    • Verify that 60% of total weight is actually in the middle half.
    • For complex cargo, use center of gravity calculation (see CTU Code appendix).
  5. Cargo securing
    • Use lashing straps, nets, wooden reinforcements or modern airbags.
    • Check that cargo cannot change position even with significant acceleration or braking.

Sample calculation:

40′ container (12 m), cargo 20 t:

  • Middle 6 m (between 3rd and 9th meter): 12 t must be here (60% of 20 t).
  • First and last 3 m: each part max. 4 t.

Exceptions, specific cases and modern technologies

SituationRecommended procedure
One heavy piece (machine, coil)Distribute weight using support beams over the largest possible area
Handling with modern spreaderAdvanced spreaders with eccentricity compensation allow tolerance up to ±10%
Fragile/uneven cargoUse precise center of gravity calculations, consult with an expert
  • Caution: Exceptions must not be abused for regular shipments!

Safety and economic consequences of non-compliance with the rule

Safety risks

  • Handling in ports: Risk of container drop, injury or death of personnel.
  • Road transport: Risk of truck tipping, infrastructure damage.
  • Rail transport: Track damage, derailment.
  • Maritime transport: Stack collapse, container loss, ship endangerment.

Economic consequences

  • Cargo and container damage: Thousands to millions of crowns in damages.
  • Supply chain delays: Costs for transshipment, storage, penalties.
  • Legal disputes and insurance claims: Insurer may refuse payment if packing error is proven.

Responsibility in the supply chain

SubjectResponsibility and tasks
PackerContainer condition inspection, correct distribution and cargo securing, issuance of loading certificate
ShipperProvision of accurate cargo data, cooperation in packing preparation
CarrierExternal condition inspection, safe container handling, transport according to declared parameters
ReceiverOpening, condition inspection and safe unloading
  • Important: Primary responsibility for compliance with the 60/50 rule always rests with the person or company that packs the cargo into the container!

Difference between Rule 60/50 and sanction rule 50%

Rule 60/50 (CTU Code)Rule 50% (sanctions, OFAC/EU)
Physical weight distributionLegal ownership structure of entity
Transport safetyCompliance with international law and sanctions
Technical standardFinancial and legal regulation

Must not be confused! The numbers are the same only by coincidence.

Recommended equipment and tips

  • Digital scales, pallet trucks with scales – accurate weighing of each pallet.
  • Software layout planners – visualization and simulation of center of gravity.
  • Quality securing material – lashing straps, airbags, fillers.
  • Checklists according to CTU Code – for each loading.

Modern trends and technologies

  • Automated cargo distribution systems – AI and IoT for real-time center of gravity detection.
  • Smart containers – sensors for monitoring cargo movement and center of gravity.
  • Online training and packing certification – available for logistics teams in the Czech Republic and abroad.

Checklist for correct cargo distribution

  • I know the exact weight of all cargo pieces
  • Distribution plan complies with rule 60/50
  • Heavy pieces are in the middle half of the container
  • Lighter pieces and fillers are at both ends
  • All gaps are filled
  • Cargo is firmly secured
  • Center of gravity check – must not exceed ±5% of container length
  • Documentation and certification in accordance with CTU Code

Rule 60/50 is the cornerstone of safe maritime transport. Its consistent compliance prevents accidents, protects values and lives and is a sign of professionalism of all links in the logistics chain. In today’s time, when the volume of container transport is growing, knowledge and application of this rule is key to successful and safe delivery of shipments worldwide.