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 carrier spec sheets quote, and the numbers to use when a booking form asks for container capacity. As a stowage rule of thumb, plan cargo against roughly 90% of the geometric figure: even uniform, floor-loaded cartons leave slivers of air at the walls and ceiling.

*The 90% column is an estimate for well-packed uniform cartons, not a specification. Geometric volumes follow ISO 668 internal dimensions and carrier spec sheets; reefer volumes are below-load-line figures. Mixed-carton loads land lower still — the next section breaks that down per size.

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. Usable CBM is what mixed cartons actually achieve once imperfect stacking, pallet decks and door clearance take their share:

Uniform carton sizes, cargo that tolerates rotation and floor-loading without pallets push utilisation toward the top of each range; 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.

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. 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 air. 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, a 40 ft HC ~375 kg per CBM. 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.