What is Break-Bulk Cargo?

Break-bulk cargo refers to goods that must be loaded individually onto a ship, rather than being placed in intermodal containers (like standard 20ft or 40ft shipping containers) or transported in bulk (like oil or grain). Common examples of break-bulk include large machinery, construction equipment, steel beams, structural timber, and oversized vehicles (RO-RO).

Understanding the W/M (Weight or Measure) Rule

Because ocean carriers have limited space (volume) and limited buoyancy (weight capacity), they charge based on whichever factor takes up more of the ship's total capacity. This is known as the W/M (Weight or Measure) Rule.

• Weight: Measured in Metric Tons (MT), where 1 MT = 1,000 kg.
• Measure (Volume): Measured in Cubic Meters (CBM).

For standard ocean freight, the ratio is 1 MT = 1 CBM. A Revenue Ton (RT) is strictly the greater of the two numbers.

Example Calculation

Imagine you are shipping a large, lightweight turbine. It weighs 25 Metric Tons (MT), but it is very bulky and takes up 60 Cubic Meters (CBM) of space.

If the freight rate is $120 per W/M, the carrier will look at both numbers:

• Cost based on Weight: 25 MT × $120 = $3,000
• Cost based on Volume: 60 CBM × $120 = $7,200

The carrier will charge based on Volume (the larger number). The chargeable "Revenue Tons" is 60 RT, and the total freight cost is $7,200.

Why Are Port and Stevedoring Fees Billed by W/M?

Unlike container shipping where ports charge a flat fee per box (THC - Terminal Handling Charge), break-bulk cargo requires specialized labor and equipment to load and secure. Cranes (stevedoring) and port storage are constrained by both weight and physical dimensions, so these secondary logistics fees almost universally apply the same W/M rule to calculate your final port bill.