Container CBM Guide

33.2 CBM in a 20 ft container, 67.7 CBM in a 40 ft, 76.4 CBM in a 40 ft high cube — those are the geometric internal volumes the published line and maker sheets print, and the numbers to use when a booking form asks for container capacity. As a stowage rule of thumb, plan cargo against roughly 85% of the geometric figure, the share the site’s calculators use: even uniform, floor-loaded cartons leave slivers of air at the walls and ceiling.

*The 85% column is a planning rule of thumb, not a specification or a standard; well-packed uniform cartons can do better. Geometric volumes are what the published line and maker sheets print — ISO 668 sets the outside of a container, not its inside; reefer volumes are below-load-line figures. Mixed-carton loads vary more, as the next section explains.

Two numbers matter per container, and quoting the wrong one is the classic booking mistake. Geometric CBM is the internal volume — what the spec sheet says, the first column of the table above. Usable CBM is what cartons actually achieve once imperfect stacking, pallet decks and door clearance take their share; the site plans against 85% of the geometric figure, the second column.

This guide gives no fixed range for mixed cartons: how far a load falls short of the geometric volume depends on the cartons themselves. Uniform carton sizes, cargo that tolerates rotation and floor-loading without pallets push utilisation up, and well-packed uniform cartons can pass 85%; fragile, odd-shaped or palletised goods pull it down. Check your own load against these ceilings in the CBM calculator, which reports fill percentage per container size, or in the container load calculator, which places every carton and gives the count a volume figure cannot.

Below a certain volume you don’t book a container at all — you ship LCL (less than container load), paying per CBM to share a box that a consolidator fills with other shippers’ cargo. FCL (full container load) is a flat rate for the whole box, empty space included.

The breakeven sits at roughly 13–15 CBM at typical rates — an estimate, not a published figure. LCL pricing stacks per-CBM charges at both ends — ocean freight, origin consolidation, destination deconsolidation and handling — and the destination fees in particular scale with volume. Somewhere around 13–15 CBM the summed per-CBM charges cross the flat FCL rate for a 20 ft, and the dedicated box wins even though you sail with 18–20 CBM of its 33.2 m³ empty. Above ~15 CBM, FCL also buys speed (no consolidation wait) and lower handling risk, since nobody restuffs your cargo en route.

Practical rule: under ~10 CBM, LCL without question; over ~15 CBM, book the 20 ft; in between, price both — the answer swings with the lane and season. Measure your shipment in the CBM calculator first, and see 20 ft vs 40 ft for the next threshold up, where a 40 ft beats two twenties.

Every container runs out of either space or weight. Divide payload by capacity: a 20 ft gives ~850 kg per CBM (28,250 kg over 33.2 m³), a 40 ft HC ~375 kg per CBM (28,670 kg over 76.4 m³). If your cargo is denser than that, weight is your constraint and volume goes unused — a key reason heavy cargo moves in 20 ft boxes.