Freeboard Calculator

Work out freeboard instantly with clear inputs, formula shown and shareable results.

About Freeboard Calculator

Freeboard is the vertical distance from the waterline to the freeboard deck: moulded depth minus draft. It is the measure of reserve buoyancy, the watertight volume above water that keeps the ship afloat when it heels or takes water on deck, which is why load line rules assign a minimum value.

Formula

Freeboard

Freeboard = moulded depth - loaded draft; reserve buoyancy ratio = freeboard / draft

Worked example

With the default values below, Freeboard Calculator returns Freeboard of 2.70. Change any input above and every figure here is recalculated in your browser.

Inputs used

Moulded depth to freeboard deck: 9.2 m
Loaded draft: 6.5 m
Length: 120 m

Results

Freeboard: 2.70 m
Freeboard as share of depth: 29.3% %
Approximate reserve buoyancy: 41.5% %
Indicative minimum freeboard: 2.60 m

Step by step

1Values used
2Freeboard
3Freeboard= 2.70 m
4Freeboard as share of depth= 29.3 %
5Approximate reserve buoyancy= 41.5 %
6Indicative minimum freeboard= 2.60 m

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 2 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

Why is minimum freeboard regulated?

Because reserve buoyancy determines survivability in heavy weather and after damage. The Load Line Convention assigns freeboard from length, type and superstructure.

What do the load line marks mean?

Each mark is the maximum draft for a zone and season — tropical, summer, winter and fresh water — reflecting different sea conditions and water densities.