Stowage

Stowage factor and broken stowage

Published 28 August 2026 · updated 22 September 2026

Stowage factor is how much room a tonne of the cargo takes up. Broken stowage is how much of the hold that same tonne renders unusable without occupying it. Both are a volume divided by a weight, both get quoted in the same units, and a broker who applies the first without allowing for the second has quoted an intake the ship cannot reach.

What a stowage factor actually measures

The stowage factor is the volume that one unit of weight of a commodity occupies as offered for shipment. It already contains the air inside the mass: the gaps between grains of wheat, the voids between lumps of coal, the space a bale of cotton does not fill because a bale is not a solid. It is a property of the parcel at the moment of loading, not a physical constant of the substance.

Two unit systems are in daily use and they do not convert cleanly. Metric quotes cubic metres per tonne. The traditional quote is cubic feet per long ton, so the conversion is about 35.9 rather than the 35.3 that converts cubic feet to a metric tonne. Half a cubic foot per tonne looks like nothing and moves a Panamax stem by hundreds of tonnes.

Those are trade conventions and a starting point for a conversation, nothing more. The shipper’s declared figure governs, and it moves with moisture, grade, origin and season.

Broken stowage is the ship’s doing, not the cargo’s

Broken stowage is the space inside the compartment that the cargo cannot use, and almost all of it is created by the ship. Frames and brackets. Hopper and topside tanks. The taper at the forward end of number one hold. Pillars, sweat battens, ladders and manholes. Dunnage laid to keep the cargo off the tank top. Tiers that do not divide evenly into the hold height, so the last one is half a tier of air.

It is expressed as a percentage of the compartment volume and it is decided by how the cargo is presented, not by what the cargo is. The same fertiliser has almost no broken stowage in bulk and a great deal of it in bags.

The three mistakes, in order of how often they are made

Using the wrong capacity. Grain capacity is measured to the full internal limits of the space, out to the frames and up into the hatch coamings, and is what a cargo that flows can use. Bale capacity is measured to the inside of the frames or the cargo battens and is what a bagged, baled or packaged cargo can use. Apply grain capacity to bags and the calculation is wrong before the stowage factor is even chosen.

Deducting broken stowage twice. Bale capacity has already taken the structure out. A modern smooth-sided bulk carrier’s grain capacity is measured to real moulded limits, so for a trimmed bulk cargo the structural loss is largely in the number already. Adding a further blanket percentage on top of a bale figure for a bagged cargo is defensible; adding one on top of a grain figure for a trimmed bulk cargo is quietly deleting cargo that exists.

Treating the published figure as a fact about this parcel. Moisture is the usual culprit. A wetter cargo weighs more per cubic metre, so the stowage factor falls, the ship deadweights out sooner, and the shipper is entitled to be surprised that the declared quantity no longer fits the ship. The same commodity out of two ports is not the same number.

What the pair actually decide

Multiply the ship’s usable capacity by the reciprocal of the stowage factor and you have the tonnage the holds will physically take. Compare it with her deadweight cargo capacity and one of two things is true: she cubes out, filling the holds before she reaches her marks, or she deadweights out, reaching her marks with space to spare. Every hull has a critical stowage factor at which those two happen together, and it is simply her capacity divided by her deadweight cargo capacity. Anything lighter cubes out; anything heavier deadweights out. It is a fixed property of the ship and it answers the volume question for every cargo she is ever offered. The arithmetic sits in what a ship can actually lift.

On breakbulk the same pair sets the freight rather than the intake. General cargo is customarily quoted per freight tonne, weight or measurement, whichever produces the greater revenue, with a cubic metre standing against a tonne. A cargo with a stowage factor above 1.0 pays on its measurement, which is another way of saying the carrier charges for the space the cargo wastes.

Where the codes take over from the cargo book

For solid bulk cargoes the stowage factor is not a commercial nicety, it is an entry in the individual schedule of the IMSBC Code, alongside the angle of repose, the cargo group and any special precautions. That schedule, and the shipper’s cargo declaration required before loading, are what the master works to. Grain is deliberately outside the IMSBC Code and lives under the International Grain Code, because for grain the governing question is not how many tonnes fit but what happens to the ship’s stability when the surface moves.

A stowage figure taken from a book is a planning number. A stowage figure on a cargo declaration is a document with consequences.

References

• International Maritime Organization, International Maritime Solid Bulk Cargoes (IMSBC) Code. IMO, cargoes in bulk
• International Maritime Organization, International Code for the Safe Carriage of Grain in Bulk (International Grain Code). IMO, Grain Code
• International Maritime Organization, Code of Safe Practice for Cargo Stowage and Securing (CSS Code). IMO, CSS Code
• G. M. Pepper (ed.), Thomas’ Stowage: The Properties and Stowage of Cargoes, 10th edition, 2024.

Related