CBM is simply cubic metres: length times width times height, with every dimension in metres. Take an export carton measuring 60 by 40 by 40 centimetres. In metres that is 0.6 × 0.4 × 0.4, which gives 0.096 CBM per carton. Five hundred of those cartons come to 48 CBM. The arithmetic never gets harder than this, but two mistakes recur: people measure the product rather than the packed carton, and people forget that pallets add height. A carton stack of 1.15 metres on a 0.15 metre pallet occupies 1.30 metres of container height, not 1.15.
Container capacity is the number you compare against. Internal volume for a standard 20ft box is roughly 33 CBM, for a 40ft standard roughly 67 CBM, and for a 40ft high cube roughly 76 CBM. Nobody achieves those figures in practice. Cartons do not tessellate perfectly, pallets waste the gaps between footprints, and the last row rarely fits. Plan on loading around 25 to 28 CBM into a 20ft, 55 to 60 into a 40ft standard, and 65 to 68 into a 40ft high cube. Against those working figures, our 48 CBM example fits comfortably into a 40ft standard and will not fit a 20ft at any packing efficiency.
Volume is only half the constraint. Every container also has a maximum payload, and dense cargo hits the weight ceiling long before it fills the space — tiles, liquids, machinery parts and printed matter are the usual offenders. Divide gross weight by CBM to get your density in kilograms per cubic metre. Cargo under about 400 kg per CBM will almost always cube out first. Cargo above roughly 800 kg per CBM is heading for a weight limit, and at that point two part-filled containers can be cheaper and safer than one overloaded one. Road weight limits on the inland leg can also be stricter than the container's own rating, which is a separate check worth making at the destination end.
For LCL, the same arithmetic decides your bill. Sea freight consolidations are charged on the weight-or-measure ratio, where one cubic metre is treated as one tonne and you pay on whichever is greater. A 10 CBM shipment weighing 6 tonnes is charged as 10 units; the same 10 CBM weighing 14 tonnes is charged as 14. Work out both figures before you ask for a rate, because a quote per cubic metre and a quote per revenue tonne are not the same quote.
Two practical habits make these numbers reliable. First, build the calculation from a packing list that states outer carton dimensions and gross weight per carton, not from estimates the supplier gives over chat. Second, recheck after the goods are actually packed — suppliers change carton sizes between orders more often than they mention it, and a five centimetre increase across 500 cartons can push you into a larger container. If you send us carton dimensions, quantities and gross weights, we will tell you which equipment fits and whether volume or weight governs the price.