Tonnage Measurements Explained

Tonnage Measurements Explained

Understanding tonnage measurements can be of critical importance during your years of boat ownership. Do you happen to know the difference between the terms Lightweight Tonnage and Net Tonnage? If not, read on! There are at least eight different ways that tonnage can be accounted for. This can depend on the type of vessel you are working with. When looking at tonnage you can be dealing with Standard Displacement Tonnage, Displacement Tonnage, Lightweight Tonnage, Gross Tonnage, Deadweight Tonnage, Net Registered Tonnage as well as Gross Registered Tonnage and Net Tonnage. That’s a lot of terms and we wouldn’t blame you if you are experiencing confusion. Here is a guide to figure out what your vessel tonnage is:


Standard Displacement Tonnage:

Standard Displacement Tonnage is that the same thing as ‘displacement tonnage” but there is a small difference that sets them apart. When you are calculating the standard tonnage you should subtract the weight of any potable water and fuel that is on board your vessel.


Displacement Tonnage

Displacement Tonnage is simple and is calculated by the total weight of the volume of water your vessel displaces as it sits in the water. To understand this better imagine you have tub filled to the brim and you get inside it. This causes water to flow over the edges and make a mess on your bathroom floor. Once the water has stopped spilled and things come to rest you have yourself the weight of the water that was being equal to the displacement of the body that entered the tub.

Tonnage Measurements Explained1

Deadweight Tonnage

Deadweight Tonnage is the weight of everything that is carried aboard the ship. This can give a commercial ship owner an idea of how much cargo he or she can safely carry and what the profit of carrying that amount of cargo will total.


Lightweight Tonnage

This tonnage is calculated by what a ship weighs when it is being built. This include and metal, wood, bolts, nuts etc. but does not include things like the fuel in the tank or potable water that is stored.


Net Tonnage

Net Tonnage is a measurement of the total internal volume of the inside of the vessel. This involves the total volume of cargo spaces in cubic meters. The calculation of net tonnage involves a ton of extra factors which makes it one of the hardest measurements to decide on.


Gross Tonnage

Gross Tonnage is the calculation of the vessels total interior volume.

Net Registered Tonnage

Net Registered Tonnage is an additional measurement of volume. However, this measurement only considered the volume of cargo storage areas but done so by dividing the cubic volume in feet by the number 100. It includes cargo holds, tanks, and anything else that is used for cargo

Now that you understand more about how cargo is measured you can be confident on how to measure your own vessel’s tonnage. If you need any assistance with filing for licences or other paperwork you can check out National Vessel Registry’s homepage for more information.