Do you know the difference between Net Tonnage and Lightweight Tonnage? By my count there are at least eight different ways a vessel’s “tonnage” is measured in regards to ships, MODUs, and other types of commercial vessels (**Displacement Tonnage**, **Standard Displacement Tonnage**, **Deadweight Tonnage**, **Lightweight Tonnage**, **Gross Tonnage**, **Net Tonnage**, **Gross Registered Tonnage**, and **Net Registered Tonnage**).

If you’re a little confused about what all these different units of measurement mean, here’s a quick guide to help straighten you out the next time someone asks you “how much your ship weighs”.

### What is Displacement Tonnage:

Displacement tonnage is nothing more than the total weight of the volume of water a ship “displaces” when it is sitting in the water.

Imagine you had a large bucket filled to the brim with water. Now, suppose you gently placed a basketball in the bucket causing some of the water in the bucket to spill out. Once the basketball had stabilized and was freely floating in the bucket, the weight of the water that was “displaced” is equal to the “displacement” (or weight) of the basketball.

### What is Standard Displacement Tonnage:

Standard displacement tonnage is basically the same thing as “displacement tonnage” with one minor difference. When calculating standard displacement tonnage, you subtract the weight of any fuel and potable water carried on board the ship.

### What is Deadweight Tonnage:

Deadweight tonnage is the weight (in tons) of all the cargo, fuel, dry provisions, supplies, etc. carried on board the ship. In other words, it is the “displacement tonnage” of the vessel minus the “lightweight tonnage” (see lightweight tonnage below). Deadweight tonnage is a good indication for ship owners and clients of how much revenue the vessel is capable of generating.

### What is Lightweight Tonnage:

Lightweight tonnage is best described as the weight of the ship when it was built in the shipyard including all framing, machinery, decking, etc. However, lightweight tonnage does not include the weight of any consumable such as fuel, water, oil, or supplies.

### What is Gross Tonnage:

Gross Tonnage is a measure of the ships total interior volume and is calculated by multiplying the interior volume “V” of the ship in cubic meters by a variable known as “K” (which varies depending on the ships overall volume).

Gross Tonnage is not to be confused with * Gross Registered Tonnage* which is explained below.

### What is Net Tonnage:

Similar to Gross Tonnage, Net Tonnage is a measure of the total interior volume of a ship’s cargo spaces and is calculated in much the same way. The total volume of designated cargo spaces in cubic meters is then multiplied by myriad factors resulting in an official net tonnage value. The actual calculation of Net Tonnage is one of the more complicated tonnages to calculated and beyond the scope of this article but takes into account factors such as moulded draft and the number of passengers a vessel is rated to carry.

Net Tonnage is not to be confused with Net Registered Tonnage which is explained below.

### What is Gross Registered Tonnage (No Longer Used):

Gross registered tonnage is a measurement of volume of all enclosed spaces on a ship with 100 cubic feet = to one ton. For instance, if the total cubic volume of all the enclosed spaces on a ship were 340,000 cubic feet, the gross registered tonnage will most likely be 3400 gross tons (340,000 cu. feet/100 cu feet/ton = 3400 Gross Tons).

The use of the term “Gross Registered Tonnage” was phased out beginning in 1969 with passage of *The International Convention on Tonnage Measurements of Ships* and hasn’t been used officially sense 1982.

### What is Net Registered Tonnage (No Longer Used):

Net registered tonnage is also a measurement of volume however you only consider the volume of actual cargo storage areas when dividing the cubic volume in feet by 100 to get your “tonnage”. This includes any tanks, cargo holds, etc. that are normally used for transporting cargo.

Hello good day sir/madam,please am so impress with your explanation on tonnage,but there one thing am searching for which i ve not yet found,please can you send me or paste it on your site,the formular for calculating the quantity of cargo in a tank by measurement either in cubic feet or cubic meter,and why is that density and specific gravity is always apply when calculating fluid like crude oil and diesel?thanks……israel

hello

Good work

Teacher of navigation and ship satbility

Thank you

Hello sir/madam

Am business man, and I have just started deals in shipping line, for buying ships, vessels, Barge, passengers ships Etc, on scrape / Demolition basis,,

What I want to know from maritime n readers, where or how i can get Right Weight for ships, or on which websites,

Because i have been cheated ones by some Brokers, and i made some Losses,

they confused me with (DWT) deadweight tons,

So i request to all of U, to how do i get the right values/ Weight of ship before i makes any new Deal in this fild, thanks

iif yiu ask for ship particulars for any vessel you want to buy it will be provided to you, it has dwt,grt, nrt and Loa of the vessel

Very useful information.

what is the difference between the ship displacement and the ship total mass? and is there any empirical formula to calculate the ship total mass from its displacement

They are one and the same – the ship will displace a mass of water precisely equal to its mass (assuming of course that it doesn’t sink!).

So a ship that displaces 1 tonne of water (1 cubic metre of fresh water) would mean that if you took it out of the water and placed it on a weighbridge, it’d weigh 1 tonne.

Can somebody tell me why, pray tell, there are no stats published for the displacement of commercial vessels – only naval vessels? I only see stats for DWT or GT. Nothing on how heavy the ship itself is.

I want to compare the actual total plimsoll line weight of a ship like the Emma Maersk vs the weight of ship like an aircraft carrier.

Thank you.

can u write some note or extra information about element of shipping?

Hello my name is Kim I work at the Inland Waterway Transport Department.

It is complicated for a measurement of a ship. When I go down to survey a ship.

I am not sure how to calculate the GT and DWT. The Displacement is OK because of

L, B, d, and the Block Coefficient. So I need the help so much. Thank you.

Best regards

How to calculate weight of a empty ship? Help Please?

I am supposed to find the weight of an empty ship for a class, but the only information i’m given is the ships Gross Register Tonnage, Net Register Tonnage, Deadweight, Cargo Capacity, Length, Breadth, and Depth. I tried wikipedia but didn’t understand what they were saying. Please help

Hello sir / madam

Pls let me know how to get a light ship weight of vessel, ship,barges etc.

Because am always getting confusion when i read (DWT)

I am new in this field for scraping /demolition ship

Now always when I ask any one for the ship details, and actul weight(Leigh ship weight ) they send me DWT weight.

So I don’t know how to get a light ship weight…

Hi Raji,

Ask them for a stability tables or trim tables, there should be the figure of Light Ship Weight. This is the weight of the ship taken from the figures when building the ship in the shipyard. If the classification society which control the ship construction is fair, they must collect all the plating’s and all other materials built in the ship with all the measurements and also weight. At the end all the parts are summed together and you get the final weight of the ship. This may be also calculated from the Displacement tables. The Displacement (D) is calculated out of the mean draft and you get the present full weight of the ship. You subtract all the remaining on board: possible water in different tanks, fuel in the fuel tanks and daily tanks in the engine room, possible lubrication oil, any remaining of cargo, any tools, paint etc in the ship stores. When you subtract all the known weights you finally can calculate also a Deadweight constant, subtract also this one and probably you will be very close to the real weight of remaining hull weight.

For a DW constant you will do the best figure if you get one of the last Draft surveys when the ship were engaged in a charter but this is usually done for bulk carriers and tankers but not for a general, cellular or similar linear ships. If you need more help and I’ll be close on holidays I may show you practical when you are going to dill a new buy.

If you have a scanned documents you may send me free for a review and I may also give to my students for a practical evaluation and send you back the best findings.

By and good luck.

Marijan

After an extended period of getting confused by all these terms, I finally understand the difference between them. Great illustration and explanation!

Which tonnage should i consider while negotiating for obsolute ship for scrap purchase

Probably a bit late for you, but lightweight tonnage will tell you the actual mass of the (empty) ship which will be the best measure for its scrap value.

Hi,

Great explanations….

I have a ship to scrap in United Arab Emirates

GT :268

NT: 80

DWT : 396

You can contact me at chris@arabiayachting.com

Thanks for stopping by my maritime blog Mr. Chris and good luck scrapping your ship!

Hi,

Very clear

I have a ship to scrap in United Arab Emirates

GT :268

NT: 80

DWT : 396

You can contact me at chris@arabiayachting.com

Thanks for stopping by my maritime blog Mr. Chris and good luck scrapping your ship!

Thank you very much for your information. I am a Senior Tonnage Surveyor for the Panama Canal, and sometimes it is very difficult to explain to others some terms. This simplifies a lot much explaining.

Thank you Hector! How are things going with the expansion of the Panama canal?

nice article, thankyou!!!!

Very Useful..Thanks

Can anyone please give some example figures? Of course every ship is different but just for the sake of comparing those terminologies, let’s suppose a new ship has 10,000 tonnes Lightweight Tonnage.

What is the probable Deadweight Tonnage? Net Registered Tonnage? Gross Registered Tonnage? Standard Displacement Tonnage?

Please only give rough numbers for the sake of illustrating this example.

Thanks

Dear Sir,

Ur explain well understood. But can u pls tell me “is the weight of lfa anf ffa incuded in lightship displacement ?” and as per which regulation?

Ben Dinsmore u r such amazng planing to bought u r offshore entry level books

Dear sir/madam,

Kindly teach me on how to determine the total iron/metal content in tonnage of a vessel. My email is (info4scores@gmail.com). I look forward to your response.

Thank you.

You are simply the best, just solved my problem.

What is the difference between PANAMA Gross tonnage and Normal Gross tonnage?

sir how can i get the ship net wight when the ship built.

i want know the wight with out fuel .oil.water and others.i want only metels used in the ship

Nice article – and I especially liked your diagrams.

Just one note – it is exceptionally rare to find anyone referring to a phrase called “Standard Displacement Tonnage” in the maritime sector.

Else, I enjoyed reading your article. Most people do not realize that gross and nett tonnage have nothing to do with weight. Many inadvertently write the gross tonnage of a ship as 12,352 tonnes – thus compounding this error.

As for Rahul’s question on Panama gross tonnage –

The ACP (Panama canal authority) has a separate set of regulations on the calculation of gross tonnage. Certain other areas of the ship are exempt and some are not, the volumes of some spaces have a different multiplier. This is a pretty detailed calculation and once done, remains with the ship for her lifetime. The ACP corelates this with the ships Panama canal identification number.

Panama canal authority uses the Panama gross tonnage to calculate the ships dues.

On the other hand, international gross tonnage calculation is done with reference to the procedures given in the International Tonnage Convention 1969.

There is no such thing as ‘Gross Register Tonnage’ (GRT) or ‘Net Register Tonnage’ any more. These terms applied to tonnage measured prior to the implementation of the International Tonnage Convention 1969. The correct terms now are ‘Gross Tonnage’ (GT) or ‘Net Tonnage’ (NT).

Thank you for the clarification, Ken. I guess I’m showing my age…

Who isa bigger displacement the ships with lenght 220 breadth 30 or the ships with lenght of 223 breadth 31 but same size panamx type

Please, Can anybody tell me…

How can I differentiate if an Oil Tanker is loaded or not?

Thanks,

Gokson

When you a tanker underway you are able to see the drf , if the vessel is not loaded you will seee most the dft scale visible, however sometime the vessl may not be Loaded with Cargo may be underway to Load Carg you will see the dft is small

Sir , how can i determine the deadmeight tonnage of a vessel by using using particulars only such as gross registered tonnage and net registered tonnage?

Sir , how can i determine the deadweight tonnage of a vessel by using using particulars only such as gross registered tonnage and net registered tonnage?

admin can u give me the formula of lightweight calculation please

Hey

A fishing troller of LDT weight 750 MT, so please tell me that the wood and cork in the vessel are they either included in the LDT or treated separately?

What is treated as wastage and it’s percentage when we cut the fishing troller?

Vessel’s gross and net weight is 950 MT & 355MT what does this means? And what items are included in gross weight?

Looking forward for your reply

Hey

A fishing troller of LDT weight 750 MT, so please tell me that the wood and cork in the vessel are they either included in the LDT or treated separately?

What is treated as wastage and it’s percentage when we cut the fishing troller?

Vessel’s gross and net weight is 950 MT & 355MT what does this means? And what items are included in gross weight?

Looking forward for your reply

Dear Faooq, as per the author explanation, GRT means the volume of all enclosures in ft converted to Tonnage at 100cubic FT per ton, but NRT IS VOLUME OF ONLY THE CARGO STORAGE AREA

I just wanna know how to calculate (or gauge) the quantity of Crude or Any Petroleum Product on a vessel to determine whether the vessel is loaded with a specific tonnage of Cargo

Hi! please could anyone help me converting GRT units to GT units? Is there any close conversion? Sincerely

Hello Sir,

Job well done .I was actually given an ssignment on this topic and your blog gives me a well simplified answer. THANK you sir!

I will be glad if I can have your person as a MENTOR in this field of study for direction because I’m very NEW in the Maritime Enviromental studies which I just started as a pgd programme at the University of Lagos,Nigeria.

PLEASE SIR,help my dream come through as I journey through the Maritime World

Warmest regards.

Hello good day sir/madam,please am so impress with your explanation on tonnage,but there one thing am searching for which i ve not yet found,please can you send me or paste it on your site,the formular for calculating the quantity of cargo in a tank by measurement either in cubic feet or cubic meter,and why is that density and specific gravity is always apply when calculating fluid like crude oil and diesel?thanks

Hi Ben,

You have provided an excellent description of the terms, with two problems – the same issue twice. The term registered (or register) is no longer used, as of the recent changes to the Tonnage Convention. As a result, you may wish to change the wording to reflect this.

Best regards, and have a wonderful day!

Thank you Neill, I have attempted to correct the article to correctly reflect Net Tonnage and Gross Tonnage.

Dear Mr. Zahid. Liquids vary in their densities. Each liquid has a different density. For example we consider the density of Fresh water as 1 t per cu. M and that of seawater as 1.025 t per cu. M then for the same level of fresh water or seawater in that tank their masses would differ. This is because of the simple fact that Mass equals the product of volume and density. Since volume of the same levels of liquids in a particular tank would be the same, their masses would be obviously be different because of their densities being different. Fuel oil density could be from 0.8 to 0.95 cubic metres per tonne whereas diesel oil density could be from 0.65 to 0.8 cubic metres per tonne. Therefore their masses in the same tank at the same levels would be different. We also know that density of a particular liquid varies with temperature. Hence we also have to use temperature correction tables called Volume Correction Factor (VCF) to the observed volume of oils in the tanks and obtain the correct density before applying to the volume and obtain the correct mass. Trust it is clear to you.

Gross Registered Tonnage hasn’t been used since 1994! Gross Tonnage is the current measure and is used without units.

Corrected, thank you Mr Ross.

STABILITY BOOKLET IS MISSING. HOW TO CALCULATE LIGHT WEIGHT FOR SCRAP

I have Submersible barge to scrape,

Light ship weight : 11404.70 ton

Pls let me know if any one interested.

GRT and NRT are total internal volume, while GT and NT are moulded volume. Your explanation mentioned above is totally wrong.

Thank you Dr Chuah, corrections have been made.