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 calculator uses the standard naval architecture formula: Displacement (t) = LBP × B × T × Cb × ρ. Accuracy depends on how well the block coefficient represents the actual hull form. For concept design it is typically within 5–10%; for final design, a full hydrostatic table is recommended.

Ship Displacement Tonnage Calculator

Name: Ship Displacement Tonnage Calculator
Availability: InStock
Author: Nham Vu

Enter hull length, beam, draft, and block coefficient to calculate light ship, deadweight, and full load displacement tonnage.

Hull Principal Dimensions

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

Length Between Perpendiculars — LBP (m)

Moulded Breadth — B (m)

Design Draft — 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)

If provided, light ship = full load displacement − DWT.

Vessel Type Presets

Enter hull dimensions to calculate displacement tonnage.

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Summary

Enter hull length, beam, draft, and block coefficient to calculate light ship, deadweight, and full load displacement tonnage.

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 the deadweight tonnage (DWT) if known, or leave it blank to skip that breakdown.
Click Calculate to see light ship displacement, DWT, and full load displacement.

Use cases

Preliminary hull weight estimation during concept design.
Cross-checking a vessel's full load displacement against classification society rules.
Teaching naval architecture students the volumetric displacement formula.
Converting between metric tons and long tons for international cargo documentation.
Estimating stability margin by comparing light ship and full load figures.
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: 2026-06-11 · Reviewed by Nham Vu