What is stowage factor?
Stowage factor is the volume that one tonne of a given cargo occupies in a ship’s hold, expressed in cubic metres per tonne (m3/t). It tells a charterer whether a cargo will fill the holds or the deadweight first, and so whether a fixture is space-limited or weight-limited.
Stowage factor is one of the first numbers a dry-bulk charterer looks up when matching a cargo to a vessel. It is not a property of the ship and not strictly a property of the commodity in isolation: it is the volume the cargo actually takes up once it is loaded, trimmed and settled in the hold, voids and all. A heavy, dense cargo such as iron ore has a low stowage factor and runs out of weight long before it runs out of space. A light, bulky cargo such as grain has a high stowage factor and fills the cubic capacity of the holds well before the ship reaches her marks. Everything downstream, the choice of vessel class, the achievable parcel size and the freight per tonne, flows from that single ratio.
The anchor reference for per-cargo stowage factors at sea is the IMSBC Code 2024 (the International Maritime Solid Bulk Cargoes Code, published by the IMO), whose individual cargo schedules quote a stowage factor or stowage-factor range for each entry alongside the bulk density and hazard classification. For the underlying naval-architecture and cargo-care treatment, a standard reference such as Thomas’ Stowage sets out how the factor is measured, why it varies and how broken stowage is allowed for.
How stowage factor is calculated
Stowage factor is a simple ratio of the space a cargo occupies to its weight. The table below sets out the definition, the related quantities and the units; the prose underneath defines each variable.
| Item | Definition / formula | Unit | Reference |
|---|---|---|---|
| Stowage factor (SF) | SF = stowage volume / cargo weight | m3/t | IMSBC Code 2024, per-cargo schedules |
| Stowage volume | Hold volume the cargo occupies as loaded and trimmed, including voids | m3 | Measured or derived from grain / bale cubic |
| Cargo weight | Mass of cargo loaded into that volume | t (metric tonnes) | Bill of lading / draught survey |
| Relationship to bulk density | SF is roughly the inverse of bulk density, adjusted upward for broken stowage | m3/t vs t/m3 | Thomas' Stowage (cargo-care reference) |
| Broken stowage factor | Volume including the unavoidable voids and dunnage space between and around the cargo | m3/t | Higher than the solid factor |
| Filled / solid stowage factor | Volume of the cargo material alone, with no allowance for voids | m3/t | Lower than the broken-stowage figure |
| Imperial stowage factor | Older quoted form, cubic feet per long ton | ft3/long ton | Conversion factor to m3/t to be verified |
The stowage factor (SF) is the stowage volume divided by the cargo weight. Stowage volume is the space the cargo actually takes up in the hold once it is loaded and trimmed, including the air gaps that no loading method can eliminate, and is normally read off the ship’s grain or bale cubic for the hold rather than measured by hand. Cargo weight is the mass loaded into that volume, taken from the bill of lading or the draught survey. The factor is the inverse of bulk density, adjusted upward: a cargo with a bulk density of about 1.4 t/m3 has a solid stowage factor near 0.71 m3/t, but the figure quoted in a schedule is a little higher because it folds in the voids. That gap between the filled or solid stowage factor and the broken stowage factor is broken stowage, treated in its own section below. Stowage factor is quoted in m3/t in modern practice; the older imperial form, cubic feet per long ton (ft3/long ton), still appears in legacy fixtures and reference tables, and converting between the two needs the conversion factor stated in the broken-stowage section, which should be verified against a current source before it is relied on.
Stowage factor across the major dry-bulk cargoes
Stowage factor is what separates the dry-bulk commodities into heavy and light cargoes, and it is the single number that decides which constraint binds first on a given ship. The comparison below ranks the major cargoes from heaviest (lowest factor) to lightest (highest factor); each cargo links through to its own page. The ranges are representative IMSBC-style values and vary with grade, moisture and particle size.
| Cargo | Stowage factor (m3/t) | Loads out first on |
|---|---|---|
| Iron ore | 0.30 to 0.50 | Deadweight (heavy, weight-limited) |
| Cement | 0.65 to 0.75 | Deadweight (heavy, weight-limited) |
| Bauxite | 0.65 to 0.85 | Deadweight on most ships |
| Coal | 1.20 to 1.50 | Either, depends on ship and grade |
| Grain | 1.30 to 1.55 | Cubic (light, measurement-limited) |
Read down the column, the spread is more than four to one between iron ore and grain, which is why the same hull carries very different parcel weights depending on what is in the hold. Iron ore at the bottom of the range fills barely a third of the cubic that grain needs for the same tonnage, so an iron-ore ship is built deep and stiff to carry weight in a small volume, while a grain or coal ship trades on cubic capacity. The crossover sits around the middle of the range: a cargo whose stowage factor matches the ship’s own cubic-per-tonne will use up weight and space at the same moment, which is the most efficient case and rarely the actual one. All five ranges are sourced to the IMSBC Code 2024 per-cargo schedules and are representative rather than contractual; a real fixture uses the surveyed factor for the specific grade and load port.
Deadweight-limited vs measurement-limited cargoes
The practical use of stowage factor is to predict, before fixing, whether a ship will load to her marks or fill her holds first. Take a representative Panamax with a grain cubic of about 85,000 m3 and a deadweight of about 76,000 t (representative figures, not a specific vessel). Her cubic-per-tonne is 85,000 / 76,000, about 1.12 m3/t. Any cargo with a stowage factor below that number fills the deadweight first; any cargo above it fills the cubic first. The worked figures below show both cases.
| Case | Cargo SF | Volume for full DWT | Weight for full cubic | Binding limit |
|---|---|---|---|---|
| Heavy cargo (iron ore) | 0.40 m3/t | 76,000 t x 0.40 = 30,400 m3 (holds part-empty) | 85,000 m3 / 0.40 = 212,500 t (far above DWT) | Deadweight-limited: loads ~76,000 t |
| Light cargo (grain) | 1.40 m3/t | 76,000 t x 1.40 = 106,400 m3 (exceeds cubic) | 85,000 m3 / 1.40 = ~60,700 t (well under DWT) | Measurement-limited: loads ~60,700 t |
For the heavy cargo at SF 0.40 m3/t, loading the full 76,000 t of deadweight needs only 76,000 x 0.40 = 30,400 m3 of hold space, against 85,000 m3 available. The ship reaches her loadline marks with the holds little more than a third full: she is deadweight-limited. For the light cargo at SF 1.40 m3/t, the holds run out first: 85,000 m3 of cubic divided by 1.40 m3/t holds only about 60,700 t before the holds are full, roughly 15,000 t short of the deadweight. The ship sails with empty deadweight she cannot use: she is measurement-limited, also called cubic-limited.
This is why charterers match cargo to ship by stowage factor before anything else. A heavy cargo wants a ship with low cubic-per-tonne so the deadweight is not wasted, and a light cargo wants a high-cubic, “big box” ship so the deadweight is not the limit. Putting grain on a deep, stiff ore carrier wastes deadweight; putting iron ore on a high-cubic ship wastes nothing but does not need the extra volume.
Broken stowage and other adjustments
The quoted stowage factor already carries an allowance for the space a cargo wastes, and that allowance is the most important non-obvious input in the calculation.
- Broken stowage is the void and dunnage space between and around the cargo that cannot be filled, expressed as the percentage difference between the solid (filled) volume of the cargo and the volume it actually occupies as loaded. For a free-flowing bulk cargo that is trimmed level it is small but never zero; for bagged or irregular cargo it is large. Broken stowage is why a schedule stowage factor is higher than the inverse of bulk density would suggest, and why the surveyed factor at the load port can differ from the book value.
- Grain cubic vs bale cubic are two different statements of a hold’s capacity. Grain cubic measures the hold to the shell and into the frame spaces, the volume available to a free-flowing bulk that runs into every corner. Bale cubic measures only to the inside of the frames and is smaller, the volume available to packaged cargo. A bulk stowage-factor calculation uses grain cubic; using bale cubic understates the capacity for a free-flowing cargo.
- Moisture and particle size both move the factor. Wetter cargo and finer particle size generally pack denser and lower the factor; coarse, lumpy or aerated cargo packs looser and raises it. This is why schedule values are ranges, not single numbers, and why the load-port survey governs the actual figure.
- The imperial conversion from cubic feet per long ton to cubic metres per tonne involves both a volume conversion (cubic feet to cubic metres) and a mass conversion (long tons to tonnes). The combined factor is roughly 0.0279 to convert ft3/long ton to m3/t (one cubic foot is 0.0283168 m3 and one long ton is 1.01605 t, giving 0.0283168 / 1.01605 = 0.02787), but this figure should be confirmed against a current naval-architecture reference before it is used in a fixture calculation.
- Fixture cubic clauses matter because the charterer warrants a cargo quantity that depends on the assumed stowage factor. If the cargo loads denser or looser than assumed, the achievable parcel changes, which is why cubic and stowage-factor assumptions are written into the recap rather than left implicit. See loading and discharge rate for how cargo quantity feeds the laytime and demurrage machinery downstream.
Common confusions about stowage factor
Stowage factor vs bulk density. The two are reciprocal-ish but not identical. Bulk density is mass per unit volume of the cargo material (t/m3); stowage factor is volume per unit mass as actually loaded (m3/t). If there were no voids, one would be the exact reciprocal of the other. Because real cargo always carries broken stowage, the stowage factor is a little higher than 1 divided by the bulk density. Quoting one as if it were simply the inverse of the other understates the space the cargo will need.
Stowage factor vs load density and tank-top strength. Load density, or tank-top strength, is the maximum weight per square metre of hold bottom that the structure can carry (tonnes per square metre). It is a structural limit, not a volume measure, and it bites on very heavy cargoes such as iron ore loaded in high cones, where the cargo could exceed the permitted load on the tank top long before the hold is full or the ship is down to her marks. Stowage factor tells you how much space a cargo needs; load density tells you whether the structure can bear the resulting weight concentration. A heavy cargo can be limited by tank-top strength rather than by deadweight or cubic, which is a third constraint distinct from the two in the worked example above.
Scope and what this page does not cover
This page explains stowage factor as a cargo property: what it is, how it is calculated, how it varies across the major dry-bulk commodities, how it decides whether a fixture is deadweight-limited or measurement-limited, and how broken stowage and related adjustments affect it. It does not provide the surveyed stowage factor for a specific grade or load port, certify a ship’s grain or bale cubic, perform the stability and loadline calculation for an actual loading plan, or replace the load-port draught survey. Those are matters for the master, the loading computer and an independent cargo surveyor, working from the actual vessel particulars and the IMSBC schedule for the specific cargo. The factors, ranges and vessel figures here are representative and not contractual values.