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Gross Register Tonnage Calculator

Work out gross register tonnage instantly with clear inputs, formula shown and shareable results.

About Gross Register Tonnage Calculator

Under the 1969 Tonnage Convention gross tonnage is a dimensionless measure of total enclosed volume, GT = K1 x V with K1 = 0.2 + 0.02 log10(V). Net tonnage applies a similar coefficient to cargo spaces only and is floored at 30% of gross tonnage. Both drive port dues, manning and survey requirements.

Formula

Tonnage

GT = (0.2 + 0.02 log10 V) x V; NT from cargo volume, minimum 0.30 x GT

Worked example

With the default values below, Gross Register Tonnage Calculator returns Gross tonnage of 5,279. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total enclosed volume
18,500 m³
Cargo space share of volume
62 %

Results

Gross tonnage
5,279 GT
Net tonnage
3,225 NT
Coefficient K1 applied
0.2853
Net to gross ratio
0.6110

Step by step

  1. 1Values used
  2. 2Tonnage
  3. 3Gross tonnage= 5,279 GT
  4. 4Net tonnage= 3,225 NT
  5. 5Coefficient K1 applied= 0.2853
  6. 6Net to gross ratio= 0.6110

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.

Frequently Asked Questions

Is tonnage a weight?

No, despite the name. Gross and net tonnage are volume-based dimensionless numbers; displacement and deadweight are the mass measures.

Why does tonnage matter commercially?

Port dues, canal tolls, pilotage, registration fees and many regulatory thresholds are all assessed on gross or net tonnage.

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