Stowage

Stowage factor and broken stowage

Published 28 August 2026 · updated 17 October 2026

Stowage factor is how much space one tonne of cargo takes up. Broken stowage is the space in the hold that is lost around that tonne and cannot be filled. Both are a volume divided by a weight, and both are quoted in the same units. If a broker uses the first and forgets the second, the intake (the amount of cargo) they quote is more than the ship can load.

What a stowage factor actually measures

The stowage factor is the volume that one unit of weight of a cargo takes up as offered for shipment. It already includes the air inside the cargo: the gaps between grains of wheat, the spaces between lumps of coal, the space a bale of cotton does not fill because a bale is not solid. It describes the cargo at the moment of loading, not a fixed physical property of the material.

Two unit systems are used every day, and they do not convert neatly. The metric system uses cubic metres per tonne. The traditional system uses cubic feet per long ton, so the conversion factor is about 35.9, not the 35.3 that converts cubic feet to a metric tonne. Half a cubic foot per tonne looks small, but it changes a Panamax cargo by hundreds of tonnes.

These are trade conventions and a starting point for discussion, nothing more. The figure the shipper declares is the one that applies, and it changes with moisture, grade, origin and season.

Broken stowage comes from the ship, not the cargo

Broken stowage is the space inside the hold that the cargo cannot use. Almost all of it comes from the ship: frames and brackets, hopper and topside tanks, the narrowing at the front end of number one hold, and pillars, sweat battens, ladders and manholes. Dunnage (timber laid to keep the cargo off the hold floor) takes space too. So does stacking: if the layers do not fit the hold height exactly, the top layer is half empty.

It is given as a percentage of the hold volume, and it depends on how the cargo is presented, not on what the cargo is. The same fertiliser has almost no broken stowage in bulk, and a lot 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 inside limits of the space, out to the frames and up into the hatch coamings. A cargo that flows can use it. Bale capacity is measured to the inside of the frames or the cargo battens. A bagged, baled or packed cargo can use only this. If you use grain capacity for bags, the calculation is wrong before you even choose the stowage factor.

Taking off broken stowage twice. Bale capacity has already removed the space taken by the structure. On a modern smooth-sided bulk carrier, grain capacity is measured to the real hull limits, so for a trimmed bulk cargo most of the structural loss is already in the number. Taking off an extra general percentage from a bale figure for a bagged cargo is reasonable. Taking one off a grain figure for a trimmed bulk cargo removes cargo that really fits.

Treating the published figure as a fact about this cargo. Moisture is the usual cause. A wetter cargo weighs more per cubic metre, so the stowage factor falls. The ship reaches its deadweight limit sooner, and the shipper may be surprised that the declared quantity no longer fits. The same cargo shipped from two different ports does not have the same figure.

What the two numbers decide together

Divide the ship’s usable capacity by the stowage factor, and you get the tonnage the holds can physically take. Compare that with the ship’s deadweight cargo capacity (the weight of cargo it can carry). One of two things is true. Either the ship cubes out, filling the holds before it reaches its load line, or it deadweights out, reaching its load line with space left over. Every ship has a critical stowage factor at which both happen together. It is simply the ship’s capacity divided by its deadweight cargo capacity. Any lighter cargo cubes out, and any heavier cargo deadweights out. It is a fixed property of the ship, and it answers the volume question for every cargo the ship is offered. The arithmetic is in what a ship can actually lift.

For breakbulk (cargo in separate pieces), the same pair sets the freight, not the intake. General cargo is usually priced per freight tonne, by weight or by measurement, whichever gives the higher freight, with a cubic metre counted as a tonne. A cargo with a stowage factor above 1.0 pays on its measurement. In other words, the carrier charges for the space the cargo takes up, not only for its weight.

Where the codes take over from the cargo book

For solid bulk cargoes the stowage factor is not just a business detail. It is an entry in the individual schedule of the IMSBC Code (the international code for solid bulk cargoes), next to the angle of repose (the steepest slope at which the piled cargo stays in place), the cargo group and any special precautions. The master works to that schedule and to the cargo declaration the shipper must provide before loading. Grain is deliberately left out of the IMSBC Code and covered by the International Grain Code. For grain, the main question is not how many tonnes fit. It is what happens to the ship’s stability when the grain surface shifts.

A stowage figure from a book is a number for planning. A stowage figure on a cargo declaration is a formal statement, and it has legal effect.

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.

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