Deadweight Tonnage
Cargo-carrying capacity: loaded minus empty displacement.
Formula
Variables
Example
Loaded 60,000 t, light 15,000 t: DWT = 45,000 t
How it works
Deadweight tonnage (DWT) tells you how much total mass a vessel can carry above its own empty weight. It is found by subtracting the ship’s lightship displacement—the mass of the vessel itself, with no cargo, fuel, ballast, passengers, or stores—from its loaded displacement, which is the total mass when the ship is fully loaded. The difference works because displacement is the weight of water the ship displaces, which equals the ship’s actual total mass at that loading condition.
When to use it
Use this formula when comparing a ship’s carrying capacity, such as in cargo planning, naval architecture, or port logistics. It is especially useful for estimating how much cargo, fuel, ballast, and supplies a vessel can take on before reaching its safe loaded condition.
Worked example, step by step
Step 1: Identify the loaded displacement: Δ_loaded = 38,500 t Step 2: Identify the lightship displacement: Δ_light = 11,200 t Step 3: Subtract lightship from loaded displacement: DWT = Δ_loaded - Δ_light DWT = 38,500 t - 11,200 t Step 4: Calculate the result: DWT = 27,300 t Final answer: The ship’s deadweight tonnage is 27,300 t.
Common mistakes to avoid
- Using gross tonnage instead of displacement
- Forgetting that DWT includes fuel, ballast, stores, crew, and cargo—not cargo alone
- Mixing up lightship displacement with empty weight that still includes consumables or ballast
Did You Know?
Deadweight includes cargo, fuel, water and crew — everything a ship can carry beyond its own hull.
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