Part I — Foundations of Freight Forwarding
Cargo Calculations — Volume, Weight & the Chargeable Unit
The arithmetic every forwarder must do in their head — CBM, volumetric weight, and the chargeable weight that decides the freight bill.
Freight is sold by space and by weight, because a carrier is constrained by both: a container or aircraft hold fills up either when it is full or when it is heavy, whichever comes first. The whole of freight pricing rests on a single idea — the carrier charges you for whichever of the two costs them more. To quote correctly you must be able to calculate both, quickly and without error.
Volume — the cubic metre (CBM)
The cubic metre (m³ / CBM) is the standard unit of cargo volume. It is found by multiplying length × width × height, with all three measured in metres:
Volume (CBM) = Length (m) × Width (m) × Height (m)
The single most common error a new forwarder makes is mixing units — measuring in centimetres and forgetting to convert. Always convert to metres first.
Worked example. A crate measures 120 cm × 80 cm × 100 cm. Convert: 1.20 m × 0.80 m × 1.00 m = 0.96 CBM. Ten such crates = 9.6 CBM — useful immediately, because LCL ocean freight is sold per CBM.
Weight — gross, net and tare
- Net weight — the goods alone.
- Tare weight — the packaging / container alone.
- Gross weight — net + tare; the total presented to the carrier.
Volumetric (dimensional) weight — the key concept
Light but bulky cargo would let a customer fill a whole aircraft or container while paying almost nothing by actual weight. Carriers prevent this with volumetric weight — a notional weight derived from the volume, so that space is paid for even when the scale reads light.
Volumetric (dimensional) weight converts a shipment’s volume into an equivalent weight using an industry conversion factor. The carrier then bills the chargeable weight — the greater of the actual gross weight and the volumetric weight.
The conversion factor differs by mode:
| Mode | Volumetric rule (the standard today) |
|---|---|
| Air freight (IATA) | 1 CBM = 167 kg (i.e. ÷ 6,000 when dimensions are in cm) |
| Road / courier | commonly 1 CBM = 333 kg (÷ 3,000 in cm) — varies by operator |
| Sea LCL | charged per CBM or per 1,000 kg, whichever is greater (the “W/M” — weight or measure — rule) |
The 2003 NAFL notes taught air volumetric weight at the older factor of 1 CBM = 1,000 kg ÷ 6 = 166.67 kg, which is still essentially correct. What has changed is enforcement and precision: carriers now capture dimensions automatically at acceptance (laser/“dim” scanners), so under-declaring volume to save freight no longer works — the system re-rates the shipment. Quote the volumetric weight honestly from the start.
Chargeable weight — the number on the invoice
The chargeable weight is the figure the freight rate is actually applied to. It is the higher of the actual gross weight and the volumetric weight.
Worked example (air). A shipment is 5 cartons, each 60 × 40 × 50 cm, total actual gross weight 90 kg. Volume per carton = 0.60 × 0.40 × 0.50 = 0.12 CBM → 5 cartons = 0.60 CBM. Volumetric weight = 0.60 × 167 = 100.2 kg. Actual = 90 kg, volumetric = 100.2 kg → chargeable weight = 100.2 kg. The cargo is billed as if it weighed 100 kg, because it takes up more space than its weight would pay for.
The weight-to-volume ratio by mode — NAFL’s core rule
The original handbook frames the whole of freight pricing around a single ratio per mode — the point at which a shipment stops being charged by weight and starts being charged by volume. This is the rule every forwarder commits to memory:
- Sea — 1 : 1 → 1 tonne = 1 CBM. Charged on weight or measure, whichever is greater (W/M).
- Land / road — 1 : 3 → 1 tonne = 3 CBM. (Some road operators now mirror air rates for ease.)
- Air — 1 : 6 → 1 tonne = 6 CBM, i.e. 1 CBM = 167 kg (1,000 ÷ 6 = 166.67).
For each mode, anything below the ratio is charged purely on weight (volume is not a factor); anything above it is charged on volume.
A note on tonnes the handbook is careful about: a short ton = 2,000 lb, a long ton = 2,240 lb, and a metric tonne = 1,000 kg. Quote in the unit your rate is expressed in and never mix them.
Worked example (NAFL-style). A shipment is 500 kg, 1.5 CBM, quoted at sea US$100/CBM and air US$0.55/kg.
- Sea (1:1): volume (1.5) exceeds weight (0.5 t), so charge by volume → 1.5 × 100 = US$150.
- Air (1:6): the weight is more than one-sixth of the volume, so charge by weight → 500 × 0.55 = US$275. Quote: US$150 sea, US$275 air.
Second example. 250 kg, 1.6 CBM.
- Sea: 1.6 × 100 = US$160.
- Air: volumetric weight = 167 × 1.6 = 267 kg → 267 × 0.55 = US$147. Quote: US$160 sea, US$147 air — here air is cheaper, because the cargo is light for its bulk. This is exactly why bulky-but-light consignments are often sent by air.
Why this matters before you quote
Every freight quote in this book — ocean, air, road — resolves to rate × chargeable unit. Get the unit wrong and the whole quote is wrong: quote too low and the shipment loses money; quote too high and you lose the customer. The arithmetic here is the foundation of Chapter 5, Freight Rates.
On an LCL or air enquiry, the first thing a WorldZone operator does with a customer’s packing list is exactly this calculation — CBM, then volumetric weight, then chargeable weight — before a rate is ever quoted. A quote built on the wrong chargeable unit is the single most common cause of a margin loss on a shipment. Do this step carefully, every time.
What to take from this chapter
- CBM = L × W × H in metres. Convert units first, always.
- Volumetric weight converts space into weight; the factor depends on the mode (air ≈ 167 kg/CBM).
- Chargeable weight = the greater of actual and volumetric. It is the number the rate is applied to.
- This arithmetic underpins every freight quote that follows.