Stowage factor (SF) is the volume in cubic metres that one metric tonne of a particular cargo occupies when stowed, expressed as m³/t. It combines the density of the commodity itself with the irregular shape and packing voids. A low SF (e.g., iron ore 0.35 m³/t) means very dense cargo; a high SF (e.g., timber 2.0 m³/t) means bulky, lightweight cargo. Planners use SF to determine whether a hold is weight-limited or volume-limited.

Broken stowage is the wasted space between packages, at hold frames, behind stanchions, and at the ends of rows — expressed as a percentage of the gross hold volume. Typical values: general cargo (boxes, crates) 10–20%, bagged cargo 5–10%, bales 8–15%, bulk grain or ore 0–3%, containers in a cell-guide hold 2–5%. The calculator default of 5% is conservative for bagged or palletised cargo.

The IMSBC Code (IMO MSC.354(92)) lists individual solid bulk cargoes with their bulk density, angle of repose, and moisture limits, but does not always provide SF in m³/t directly. Commercial SFs quoted by shippers are typically based on stowed volume including packing, whereas IMSBC bulk density figures are for the cargo in isolation. For IMSBC cargoes, use the listed bulk density to derive SF = 1 ÷ bulk density (t/m³).

A hold is weight-limited when the cargo density is so high that the mass reaches the structural deadweight limit before the hold volume is filled — common for iron ore, steel, and heavy aggregates. It is volume-limited when the cargo is light or bulky and fills the hold space before reaching deadweight — common for grain, timber, and containers with light stuffing. Planners must solve for the binding constraint for each hold.