The Verified Gross Mass (VGM) is usually discussed from the shipper's side: who weighs the box and how to fill in the declaration. This guide looks at the VGM from the stowage planner's desk. For a planner, the VGM is the weight that drives stack weights, stability, drafts and lashing forces. When it arrives late, is wrong, or differs a lot from the booking weight, the vessel plan suffers.

The legal basis, the weighing methods and a sample declaration for shippers are covered in full in our VGM SOLAS guide. Here we only recap them and then follow the VGM into the stowage plan.

SOLAS VI/2 recap: method 1 and method 2

Since 1 July 2016, SOLAS Chapter VI Regulation 2 requires the gross mass of a packed container to be verified before it is loaded. The shipper named on the transport document is responsible for providing the VGM. The master and the terminal must not load a packed container without one.

Method How it works Planner's note
Method 1 The packed and sealed container is weighed as a whole on calibrated, certified equipment (weighbridge, load cell on a crane or lifting device) Usually closest to the real weight, including dunnage and securing material inside
Method 2 All packages, pallets, dunnage and securing material are weighed and added to the container tare mass, using a method approved by the authority of the state where packing was completed Prone to errors when packing material is forgotten or the tare is misread

In Indonesia the competent authority is the Directorate General of Sea Transportation. Shippers and forwarders can prepare their data with the VGM form. Enforcement tolerances are set by each administration, so the thresholds discussed below are operational company settings, not IMO values.

VGM vs booking weight as a company setting

The booking weight is the shipper's estimate when space is requested, often rounded or copied from an earlier order. The VGM arrives later, usually close to the cut-off. The gap between the two is a useful risk signal: a large difference may point to a typing error, the wrong container or cargo that changed.

A good planning system does not hard-code one threshold. It stores the thresholds as editable company settings. The following values are illustrative only:

Condition Example threshold Suggested action
Small difference ≤ 3% and ≤ 0.5 t Accept the VGM, no action
Medium difference 3–5% or 0.5–1 t Flag for planner review; recheck the weight position
Large difference > 5% or > 1 t Query the shipper or agent; recalculate the stack
Above maximum gross VGM > max gross on the CSC plate Reject and Hold; the box must not be loaded
No VGM Not received at cut-off Hold; roll to the next vessel if still missing

Using both a percentage and a tonnage threshold avoids two extremes. A percentage alone is too loose for heavy boxes, while tonnage alone is too strict for light ones. The maximum gross mass can be checked with the container payload calculator.

The Hold status: no VGM, no load

The "no VGM, no load" principle is easiest to enforce as a status in the system. A container without a VGM may receive a provisional slot in the pre-plan, but it carries a Hold status so that it:

  • is excluded from the final load list sent to the terminal;
  • is marked differently in the bay view so the chief officer and terminal planner can see it;
  • is released automatically once a valid VGM arrives, and is then included in the recalculation;
  • moves to the roll-over list if the VGM is still missing at cut-off.

What should not happen is replacing a missing VGM with the booking weight to make the plan look complete. The plan then appears finished while resting on an unverified number.

VERMAS and the VGM data flow

VGMs arrive through carrier portals, email or EDI. The standard EDI format is VERMAS (Verified Gross Mass), a UN/EDIFACT message whose implementation guide was developed by the carrier and terminal community, including SMDG. It carries the container number, the VGM value and unit, the weighing method, the responsible party and authorised signatory, and the weighing date, among other fields.

Once verified, the VGM travels to the next port inside the BAPLIE so the destination terminal works with the same number. Minimum checks on import: the container number passes its check digit, the unit is clear (kg or t), the method is filled in, and the VGM is not below the tare.

Effect of the VGM on stack weights and stability

Every stack on deck and in the hold has a weight limit, for example for the hatch cover or tank top, and the limits differ for 20' and 40' stacks. The figures are in the Cargo Securing Manual and ship documents. An illustrative five-tier 40' stack on deck:

  • Booking weights: 5 × 24.0 t = 120.0 t, exactly at the example stack limit of 120 t.
  • VGMs: 26.5 + 27.0 + 25.0 + 26.0 + 26.5 = 131.0 t, or 11 t over the limit.

A stack that looked safe on booking weights is in fact overloaded. Lashing forces rise as well, especially when the heavy boxes sit in the upper tiers. Use the container stowage calculator to check the weight order in a stack.

The stability effect becomes clear when small errors occur over many containers. An illustrative feeder:

Parameter Before VGM After VGM
Displacement 20,000 t 20,450 t
Extra weight on deck — 300 boxes × 1.5 t = 450 t, VCG 20.0 m
KG 9.00 m (20,000 × 9.00 + 450 × 20.0) / 20,450 = 9.24 m
KM (assumed constant) 9.90 m 9.90 m
GM 0.90 m 0.66 m
Extra draft (TPC 35 t/cm) — 450 / 35 ≈ 12.9 cm

KM is held constant here for simplicity; in practice it changes with draft and must be read from the ship's hydrostatic tables. The message stands: 1.5 t per box takes about a quarter of a metre off the GM. GM is explained in our guide to metacentric height, and you can try a quick figure with the basic GM calculator.

The VGM workflow in STOWAGE.ID

In STOWAGE.ID Vessel Stowage, the VGM is a container attribute. Discrepancy thresholds live in the company settings, the Hold status is applied automatically, and stack weights and GM are recalculated whenever a VGM changes. STOWAGE.ID is a shore-side planning and decision-support tool. The ship's class-approved loading computer and stability booklet remain the official reference, and the final decision rests with the master and chief officer.

Practical steps for a planning team:

  1. Agree percentage and tonnage thresholds with the commercial and operations teams.
  2. Send VGM reminders to shippers before the cut-off, not after it.
  3. Review the list of large discrepancies per port of loading before the final plan.
  4. Recheck the heaviest stacks and the GM once all VGMs are in.
  5. Keep a history of VGM changes for audits and claims.

To practise, open the demo and change the weight of one deck stack to see the effect on the stack limit and the GM.