Ship Tonnage Calculator (GT/NT)
Calculate Gross Tonnage (GT) and Net Tonnage (NT) based on the 1969 Tonnage Convention.
Input Parameters
Enter the required ship particulars. All volumes in m³, dimensions in meters.
For Gross Tonnage (GT)
For Net Tonnage (NT)
NT calculation requires a valid GT and the parameters below.
**Note:** This calculator is based on the International Convention on Tonnage Measurement of Ships, 1969. Ensure input values are correct as per vessel's official documentation. For official certification, always refer to classifications societies and authorized bodies.
About Ship Tonnage Calculator (GT/NT)
Volume-Based Measurement Standards
Tonnage is a unitless index used to represent the overall size (Gross Tonnage) or the useful capacity (Net Tonnage) of a vessel. Since the 1969 International Convention on Tonnage Measurement, these figures have been the global standard for determining a ship's regulatory obligations, including manning scales, pilotage fees, and insurance premiums.
Key Regulatory Formulas
1. Gross Tonnage (GT):
GT = (0.2 + 0.02 × log₁₀(V)) × V
2. Net Tonnage (NT):
NT = [K₂ × Vc × (4d/3D)²] + [K₃ × (N1 + N2/10)]
Where V = Total volume, Vc = Cargo volume, D = Depth, d = Draught, N = Passengers
Difference Between GT and NT
- Gross Tonnage (GT): Accounts for the volume of all enclosed spaces on the ship from keel to funnel. It represents the total magnitude of the vessel.
- Net Tonnage (NT): Specifically represents the volume of the ship's earning spaces (cargo and passengers). It is usually about 30% to 60% of the Gross Tonnage.
- Limits: According to the convention, NT cannot be less than 30% of GT.
How to Use This Tool
This calculator is intended for naval architects, ship brokers, and maritime students to estimate a vessel's registry profile. You will need the "Moulded Volume" data from the ship's lines plan or existing International Tonnage Certificate (ITC).