What is displacement tonnage?

Displacement tonnage is the mass of water displaced by a floating vessel, which equals the mass of the vessel itself (by Archimedes' principle). It is measured in metric tons (1 metric ton = 1,000 kg) or long tons (1 long ton ≈ 1,016 kg). Full load displacement includes the hull, machinery, fuel, crew, cargo, and stores.

What is the block coefficient (Cb)?

The block coefficient is the ratio of the underwater hull volume to the bounding rectangular box (L × B × T). A Cb of 1.0 would be a perfect rectangular barge. Typical values range from 0.50 for fast naval vessels to 0.85 for slow bulk carriers. The formula is: Volume = LBP × B × T × Cb.

What is the difference between light ship and full load displacement?

Light ship displacement (also called lightship weight or LWT) is the mass of the vessel with all its permanent equipment but without cargo, fuel, stores, or crew. Full load displacement adds the deadweight tonnage (DWT) — the total carrying capacity — on top of the light ship weight.

Why is salt water density 1.025 t/m³?

Standard ocean salt water has a salinity of about 3.5%, giving a density of approximately 1.025 metric tons per cubic meter (1,025 kg/m³). Fresh water is 1.000 t/m³. A vessel will sit slightly deeper in fresh water because it must displace a larger volume to achieve the same upward buoyant force.

What is deadweight tonnage (DWT)?

Deadweight tonnage is the maximum load a vessel can carry, including cargo, fuel, ballast water, fresh water, provisions, and crew. It equals the difference between full load displacement and light ship displacement. DWT is the primary commercial capacity measure for cargo ships.

How accurate is this calculator?

The formula is Displacement (t) = LBP × B × T × Cb × ρ. Its reliability depends entirely on using a block coefficient that matches the same draft and hull condition. Real hull geometry, appendages and trim are simplified, so use approved hydrostatic data for operational or regulatory work.

Ship Displacement Tonnage Calculator

Enter LBP, breadth, mean draft, block coefficient, and water density to estimate displacement at that draft. This is weight, not Gross Tonnage (GT).

Hull Principal Dimensions

All measurements in meters. Water density in t/m³.

Length Between Perpendiculars — LBP (m)

Moulded Breadth — B (m)

Mean Draft at Condition — T (m)

Block Coefficient — C_b (0.40 – 0.95)

Typical: 0.50 fast vessel · 0.65 container · 0.74 tanker · 0.82 bulk carrier

Water Density — ρ (t/m³)

Known Deadweight Tonnage — DWT (t) (optional)

Must correspond to the same entered draft. Estimated lightweight = displacement at condition − DWT.

Vessel Type Presets

Enter hull dimensions to calculate displacement tonnage.

Displacement is not Gross Tonnage. Displacement and DWT are mass measures. GT and NT are dimensionless regulatory measures derived from enclosed-space volumes under the IMO tonnage convention. Use approved hydrostatic data and survey records for vessel decisions. IMO tonnage reference

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Summary

Enter LBP, breadth, mean draft, block coefficient, and water density to estimate displacement at that draft. This is weight, not Gross Tonnage (GT).

How it works

Enter the Length Between Perpendiculars (LBP) in meters.
Enter the moulded breadth (B) and design draft (T) in meters.
Enter the block coefficient (Cb) — typically 0.50 to 0.85 for commercial vessels.
Optionally adjust the water density (1.025 t/m³ for salt water, 1.000 for fresh water).
Enter deadweight only if it belongs to the same draft/loading condition, or leave it blank.
Click Calculate to see underwater volume and estimated displacement at the entered draft.

Use cases

Preliminary hull weight estimation during concept design.
Checking preliminary dimensions against a known displacement before using hydrostatic tables.
Teaching naval architecture students the volumetric displacement formula.
Converting between metric tons and long tons for international cargo documentation.
Exploring how draft, density, and block coefficient affect a preliminary displacement estimate.
Evaluating block coefficient impact on cargo capacity for bulk carrier design.
Quick sanity-check of displacement figures in ship sale and purchase negotiations.
Comparing displacement at different draft values for ballast condition planning.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu

Ship Displacement Tonnage Calculator

Hull Principal Dimensions

Weight Breakdown

Formula Used

Summary

How it works

Use cases

Frequently Asked Questions

Ship Displacement Tonnage Calculator

Use the Ship Displacement Tonnage Calculator

Hull Principal Dimensions

Weight Breakdown

Formula Used

Summary

How it works

Use cases

Frequently Asked Questions