Deadweight tonnage (DWT) is the maximum weight a ship can carry — cargo, fuel, fresh water, stores, and crew combined — representing the vessel’s actual carrying capacity rather than its physical size.
How DWT Is Calculated
DWT = Loaded displacement − Light displacement
In other words, it’s the difference between the ship’s total weight when loaded to its maximum permitted draft, and the ship’s own weight with nothing aboard.
Why DWT Is the Standard Commercial Figure
Unlike GT and NT (which measure volume), DWT directly reflects how much weight a vessel can actually carry — which is what matters most commercially for chartering, freight calculation, and comparing vessels’ cargo capacity. When you see a ship described as “180,000 DWT,” this tells you its maximum carrying capacity in metric tons.
DWT and Ship Classification
Bulk carrier and tanker size categories (Handysize, Panamax, Capesize, VLCC, etc.) are typically defined by DWT ranges, since carrying capacity is the commercially relevant measure for these cargo-focused vessel types.
DWT vs Displacement
- Displacement — the ship’s total actual weight at any given loading condition
- DWT — the maximum additional weight the ship can carry beyond its own light weight
A vessel’s displacement changes throughout a voyage as fuel is consumed and cargo is loaded/discharged; its DWT is a fixed design characteristic of the vessel.
Exam Relevance
DWT calculation and its relationship to displacement, light weight, and cargo capacity are foundational Ship Stability and Ship Knowledge topics in deck officer competency exams.