Subscribe to our Mailing Lists (It's free!)
Friday, June 9, 2023
SAFETY4SEA
  • Home
  • Safety
    • All
    • Accidents
    • Alerts
    • Loss Prevention
    • Maritime Health
    • Regulation
    • Safety
    • Seafarers
    • Security
    NTSB Investigation

    Lessons learned: Loss of redundancy in diving bell launch and recovery PLC system

    Lessons learned: Steam and water released from filter

    Lessons learned: Disposable vape self-ignition

    maritime mental health

    Seafarers Happiness Index 2023Q1: Seafarers are unsatisfied with onboard fitness and health benefits

    Cargo fires: An issue that needs to be tackled

    Cargo fires: An issue that needs to be tackled

  • SEAFiT
    • All
    • Intellectual
    • Mental
    • Physical
    • Social
    • Spiritual
    Book Review: A role model for ship managers

    Book review: The politics of sustainability in the Arctic

    contemplation as a spiritual practice

    Contemplation: Directing the mind towards what’s important

    power of hug

    The power of hugging: How it affects our health

    Impostor Syndrome

    Mental Health Focus: How to deal with Impostor Syndrome

  • Green
    • All
    • Arctic
    • Ballast
    • Emissions
    • Fuels
    • Green Shipping
    • Pollution
    • Ship Recycling
    • Technology
    HHI wins AiP from KR for tank shape optimized for liquefied fuels

    HHI wins AiP from KR for tank shape optimized for liquefied fuels

    Four major parties to assess emissions throughout the life cycle of LNG carrier

    Four major parties to assess emissions throughout the life cycle of LNG carrier

    Port of Klaipeda and Proman shake hands on methanol bunkering

    Port of Klaipeda and Proman shake hands on methanol bunkering

    USA law

    U.S. Senators introduce legislation to eliminate in-port ship emissions

  • Smart
    • All
    • Connectivity
    • Cyber Security
    • E-navigation
    • Energy Efficiency
    • Maritime Software
    • Smart
    Cyber security: What it means for the shipping industry

    Cyber security: What it means for the shipping industry

    DNV Maritime Cyber Priority 2023: Shipping faces 5 major cyber security challenges

    DNV Maritime Cyber Priority 2023: Shipping faces 5 major cyber security challenges

    New Mission to Seafarers app strengthens welfare support

    New Mission to Seafarers app strengthens welfare support

    ABS awards AIP to SHI for structural health monitoring system

    ABS awards AIP to SHI for structural health monitoring system

  • Risk
    • All
    • CIC
    • Detentions
    • Fines
    • PSC Case Studies
    • PSC Focus
    • Vetting
    AMSA bans second vessel in a week

    AMSA bans second vessel in a week

    Ship detentions in Paris MoU in February 2021

    AMSA bans bulk carrier Babuza Wisdom for 90 days

    tanker arrested in singapore

    AMSA convicts master and company after pilot ladder injury

    amsa planned maintenance fic

    OCIMF Annual Report 2023: Key amendments and additions under SIRE 2.0

  • Others
    • All
    • Diversity in shipping
    • Maritime Knowledge
    • Offshore
    • Ports
    • Reports
    • Shipping
    • Sustainability
    • Videos
    baltic exchange

    Baltic Exchange: Maritime market highlights 5 – 9 June

    Port of Klaipeda and Proman shake hands on methanol bunkering

    Port of Klaipeda and Proman shake hands on methanol bunkering

    StenaRoRo’s ESG reporting making leaps due to Mercy Ships partnership

    StenaRoRo’s ESG reporting making leaps due to Mercy Ships partnership

    IWSA opens voting for “Wind Ship – the Future” poster design contest

    IWSA opens voting for “Wind Ship – the Future” poster design contest

  • Columns
    The tides are changing at Alang

    The tides are changing at Alang

    Ship recycling: A solution for plastic pollution and environmental protection

    Ship recycling: A solution for plastic pollution and environmental protection

    Back To The Future: How Rotor Sails are now a credible option to tackle climate challenge

    Back To The Future: How Rotor Sails are now a credible option to tackle climate challenge

    Trending Tags

    • Book Review
    • Career Paths
    • Industry Voices
    • Interviews
    • Maripedia
    • Maritime History
    • Resilience
    • Seafarers Stories
    • SeaSense
    • Wellness Corner
  • Events
  • Plus
No Result
View All Result
  • Home
  • Safety
    • All
    • Accidents
    • Alerts
    • Loss Prevention
    • Maritime Health
    • Regulation
    • Safety
    • Seafarers
    • Security
    NTSB Investigation

    Lessons learned: Loss of redundancy in diving bell launch and recovery PLC system

    Lessons learned: Steam and water released from filter

    Lessons learned: Disposable vape self-ignition

    maritime mental health

    Seafarers Happiness Index 2023Q1: Seafarers are unsatisfied with onboard fitness and health benefits

    Cargo fires: An issue that needs to be tackled

    Cargo fires: An issue that needs to be tackled

  • SEAFiT
    • All
    • Intellectual
    • Mental
    • Physical
    • Social
    • Spiritual
    Book Review: A role model for ship managers

    Book review: The politics of sustainability in the Arctic

    contemplation as a spiritual practice

    Contemplation: Directing the mind towards what’s important

    power of hug

    The power of hugging: How it affects our health

    Impostor Syndrome

    Mental Health Focus: How to deal with Impostor Syndrome

  • Green
    • All
    • Arctic
    • Ballast
    • Emissions
    • Fuels
    • Green Shipping
    • Pollution
    • Ship Recycling
    • Technology
    HHI wins AiP from KR for tank shape optimized for liquefied fuels

    HHI wins AiP from KR for tank shape optimized for liquefied fuels

    Four major parties to assess emissions throughout the life cycle of LNG carrier

    Four major parties to assess emissions throughout the life cycle of LNG carrier

    Port of Klaipeda and Proman shake hands on methanol bunkering

    Port of Klaipeda and Proman shake hands on methanol bunkering

    USA law

    U.S. Senators introduce legislation to eliminate in-port ship emissions

  • Smart
    • All
    • Connectivity
    • Cyber Security
    • E-navigation
    • Energy Efficiency
    • Maritime Software
    • Smart
    Cyber security: What it means for the shipping industry

    Cyber security: What it means for the shipping industry

    DNV Maritime Cyber Priority 2023: Shipping faces 5 major cyber security challenges

    DNV Maritime Cyber Priority 2023: Shipping faces 5 major cyber security challenges

    New Mission to Seafarers app strengthens welfare support

    New Mission to Seafarers app strengthens welfare support

    ABS awards AIP to SHI for structural health monitoring system

    ABS awards AIP to SHI for structural health monitoring system

  • Risk
    • All
    • CIC
    • Detentions
    • Fines
    • PSC Case Studies
    • PSC Focus
    • Vetting
    AMSA bans second vessel in a week

    AMSA bans second vessel in a week

    Ship detentions in Paris MoU in February 2021

    AMSA bans bulk carrier Babuza Wisdom for 90 days

    tanker arrested in singapore

    AMSA convicts master and company after pilot ladder injury

    amsa planned maintenance fic

    OCIMF Annual Report 2023: Key amendments and additions under SIRE 2.0

  • Others
    • All
    • Diversity in shipping
    • Maritime Knowledge
    • Offshore
    • Ports
    • Reports
    • Shipping
    • Sustainability
    • Videos
    baltic exchange

    Baltic Exchange: Maritime market highlights 5 – 9 June

    Port of Klaipeda and Proman shake hands on methanol bunkering

    Port of Klaipeda and Proman shake hands on methanol bunkering

    StenaRoRo’s ESG reporting making leaps due to Mercy Ships partnership

    StenaRoRo’s ESG reporting making leaps due to Mercy Ships partnership

    IWSA opens voting for “Wind Ship – the Future” poster design contest

    IWSA opens voting for “Wind Ship – the Future” poster design contest

  • Columns
    The tides are changing at Alang

    The tides are changing at Alang

    Ship recycling: A solution for plastic pollution and environmental protection

    Ship recycling: A solution for plastic pollution and environmental protection

    Back To The Future: How Rotor Sails are now a credible option to tackle climate challenge

    Back To The Future: How Rotor Sails are now a credible option to tackle climate challenge

    Trending Tags

    • Book Review
    • Career Paths
    • Industry Voices
    • Interviews
    • Maripedia
    • Maritime History
    • Resilience
    • Seafarers Stories
    • SeaSense
    • Wellness Corner
  • Events
  • Plus
No Result
View All Result
SAFETY4SEA

Do you know what GT and DWT measure in a ship?

by The Editorial Team
November 10, 2021
in Maritime Knowledge
singapore border measures

Credit: Shutterstock

FacebookTwitterEmailLinkedin

Professionals across the shipping industry may be familiar with the terms like “gross tonnage”, “deadweight tonnage”, “net tonnage” and many more terms we regularly meet in shipping-related sources, but those are not always easy to distinguish, especially when being new in the industry. Have you ever wondered what is the difference between gross and deadweight tonnage?

Tonnage 

Broadly speaking, ‘tonnage’ measures a ship’s size and can be expressed in terms of either volume or weight. 

Gross tonnage / Counted in: No unit   

RelatedNews

Do you know what FSRUs are?

American Club experiences a positive 2023 renewal season

Gross tonnage (GT or gt) is a measure of a ship’s overall internal volume and is determined by dividing by 100 the contents, in cubic feet, of the vessel’s enclosed spaces. GT applies to the vessel, not to cargo. It measures the ship’s volume and has nothing to do with weight. It is based on two variables: V, the ship’s total volume in cubic metres (m3), and K, a multiplier based on the ship volume. 

Net Tonnage / Counted in: No unit    

GT is often confused with Net Tonnage, which is a ship’s gross tonnage minus the space occupied by accommodations for crew, by machinery, for navigation, by the engine room and fuel. This means a vessel’s net tonnage represents the available space for accommodation of passengers and stowage of cargo.  

Note: GT and NT are dimensionless so they cannot be counted in physical units of tonnage. The word “tons” is no longer in use in reference to ships’ tonnage. So, we typically say “the ship has Gross Tonnage of 12,345” without the addition of any units.  

GET THE SAFETY4SEA IN YOUR INBOX!

Deadweight tonnage / Counted in: metric tonnes (1,000 kg) 

Simply put, deadweight tonnage (DWT) is a measure of how much weight a ship can carry, so it includes the sum of the weights of cargo, fuel, fresh water, ballast water, provisions, passengers, and crew. This measurement does not include the empty weight of the ship, which means that DWT represents the difference between the number of tons of water a vessel displaces “light” and the number of tons it displaces when submerged to the “load line.” As you probably remember, load lines (also known as Plimsoll lines) on a ship’s hull indicate the maximum depth to which the vessel may be safely immersed when loaded with cargo.  

‘Gross Tonnage’ = overall size of a ship 
‘Net Tonnage’ = useful capacity of a ship
‘Deadweight tonnage’ = carrying capacity of a ship in tonnes 

Displacement 

A ship’s displacement, as the word indicates, is the volume of water it displaces when it is floating and is measured in cubic metres (m3). The displacement tonnage is the weight of the water that it displaces when it is floating with its fuel tanks full and all stores onboard, and is measured in metric tons (1,000 Kg). The term “displacement tonnage” maybe seen describing the weight of the vessel and its contents in tons of 2,240 pounds. Displacement “light” is the weight of the vessel without stores, bunker fuel, or cargo, while displacement “loaded” is the weight of the vessel including all the above.  

Regulatory landscape at a glance 
The Gross and Net Tonnage measurement was established by the IMO’s International Convention on Tonnage Measurement of Ships. First adopted in 1969 and set into force in 1982, the Convention was the first successful attempt to introduce a universal tonnage measurement system. Previously, various systems were used to calculate the tonnage of merchant ships but there were significant differences in them, so the Convention addressed the need for a globally accepted system.

The Convention provides for gross and net tonnages, both of which are calculated independently. The rules apply to all ships built on or after 18 July 1982 – the date of entry into force. The Convention meant a transition from the traditionally used terms gross register tons (GRT) and net register tons (NRT) to gross tonnage (GT) and net tonnage (NT).  

Why are these useful?  

GT is not a really usable measure in everyday life, but it forms the basis for authorities, PSC and flag states, as well as classification societies to set manning regulations, safety rules, as well as registration fees. Both gross and net tonnages are also used to calculate port dues. According to Steamship Mutual P&I Club, Tonnage Measurement is used in the assessment of the following: 

  • Harbour Dues – which can be based on either Gross or Net Tonnage 
  • Pilotage Dues – which can be based on either Gross or Net Tonnage 
  • Light Dues – usually based on Net Tonnage 
  • Canal Dues – usually based on Net Tonnage 

Sometimes, the term can also be used to compare ships in terms of their size, even though a larger ship does not necessarily have also a bigger gross tonnage. To put Gross Tonnage into context, currently the world’s largest container ships by GT have a GT of just over 230,000 and the largest cruise ships by GT have just over 228,000.  

Did you know? 
Before the IMO Convention, the traditionally used terms were gross register tonnage (GRT), measuring the volume of only certain enclosed spaces, typically above the deck of a merchant ship which were available for cargo, stores, fuel, passengers and crew. Accordingly, the net register tonnage (NRT) used to measure the volume of cargo the vessel can carry, minus the spaces that do not hold cargo.

DO YOU KNOW?: Read in this series

Do you know what FSRUs are?

Do you know what FSRUs are?

March 31, 2023
gemba walk

Do you know what a Gemba walk is?

December 7, 2022
Do you know why ballasting and deballasting are vital for a ship?

Do you know why ballasting and deballasting are vital for a ship?

October 6, 2022
catzoc

Do you know what CatZoc is?

September 2, 2022
iacs

Do you know what VDR is?

August 25, 2022
Do you know how ships are protected from lightning?

Do you know how ships are protected from lightning?

August 1, 2022
singapore Maritime Welfare Fee

Do you know what makes a maritime center?

July 18, 2022
Do you know how climate change relates to shipping?

Do you know how climate change relates to shipping?

July 12, 2022
barnacle fouling

Do you know what biofouling is?

July 11, 2022
onboard carbon capture

Do you know what CII stands for?

June 27, 2022
australia singapore green economy

Do you know what EU Taxonomy is?

June 27, 2022
Green Ray

Do you know what methane slip is?

May 12, 2022
general average

Do you know what General Average means?

May 10, 2022
eunavfor

Do you know where the food you eat comes from?

April 21, 2022
nato shipping centre

Do you know what FOC are?

March 28, 2022
Do you know what the Northern Sea Route is?

Do you know what the Northern Sea Route is?

March 24, 2022
Do you know why a ship’s bow thruster is vital?

Do you know why a ship’s bow thruster is vital?

March 2, 2022
uk us energy security

Do you know what Poseidon Principles stand for?

February 14, 2022
northstandard

Do you know why P&I Clubs are vital for shipping?

December 30, 2021
singapore border measures

Do you know what GT and DWT measure in a ship?

November 10, 2021
ship

Do you know what ships apply SOLAS?

October 29, 2021
low draft limits barranquilla

12 nautical terms to know

October 22, 2021
under keel clearance

Do you know what under keel clearance is? 

October 8, 2021
sire 2.0

Do you know how ship propulsion has changed?

June 1, 2021
NATO phonetic alphabet

Do you know what NATO phonetic alphabet is?

November 24, 2020
gmdss

Do you know what GMDSS stands for?

October 22, 2020
us cruise ships

Do you know what cold ironing is?

October 5, 2020
Do you know what the bulbous bow is for?

Do you know what the bulbous bow is for?

February 6, 2020
old ships

Do you know what happens to a ship when it’s too old to sail anymore?

February 4, 2020
Ship Security Alert System

Do you know what a Ship Security Alert System is?

January 22, 2020
Authorized Service Providers

Do you know how many types of lifeboats exist?

January 17, 2020
flush the toilet

Do you know what happens after you flush the toilet on a ship?

January 16, 2020
master alternative quay

Do you know how many ranks and duties exist onboard? 

December 20, 2019
types of ships

Do you know how many types of ships exist?

December 4, 2019
bimco world fleet

Do you know why IMO number is important for vessels?

December 3, 2019
solas

Do you know when to abandon a ship?

December 3, 2019
panama shipping decarbonization

Do you know how to distinguish an Aframax from a Panamax vessel?

November 21, 2019
bunkering

Do you know what a Bunker Delivery Note includes?

November 20, 2019
emissions from ships

Do you know why FONAR is needed from 2020 and onwards?

October 23, 2019
Plimsoll lines

Do you know what Plimsoll lines on ships are?

October 17, 2019
ships are red

Do you know why ships are red on bottom?

October 16, 2019
starboard

Why do ships use ‘port’ and ‘starboard’ and not ‘left’ or ‘right’

August 18, 2019
pandemic seafarers

Inert Gas onboard: Key safety precautions

May 10, 2019
scottish maritime sector

Do you know why is a ship called she?

April 1, 2019
Tags: Do you knowMaripediatonnage

Comments 5

  1. Boy javier says:
    1 year ago

    Very informative..

    Reply
  2. KAMLESH PATEL says:
    1 year ago

    useful article

    Reply
  3. Juan Cosme says:
    11 months ago

    How do I calculate the actual weight of the vessel?

    Reply
    • David says:
      10 months ago

      each ship has displacement tonnage tables. that is, the amount of water it carries when the ship is empty. You can find this on the ship chart by looking behind the plimsol m.

      Reply
  4. Malik Humayoun says:
    8 months ago

    Great information

    Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Recommended

NTSB Investigation

Lessons learned: Loss of redundancy in diving bell launch and recovery PLC system

June 9, 2023
baltic exchange

Baltic Exchange: Maritime market highlights 5 – 9 June

June 9, 2023
MARITIME EVENTS

Explore

  • Safety
  • SEAFiT
  • Green
  • Smart
  • Risk
  • Others
  • SAFETY4SEA Events
  • SAFETY4SEA Plus Subscription

Useful Links

  • About
  • Disclaimer
  • Editorial Policies
  • Advertising
  • Contact

© 2021 SAFETY4SEA

No Result
View All Result
  • Safety
    • Accidents
    • Alerts
    • Loss Prevention
    • Maritime Health
    • Regulation
    • Safety
    • Seafarers
    • Security
  • SEAFiT
    • Intellectual
    • Mental
    • Physical
    • Social
    • Spiritual
  • Green
    • Arctic
    • Ballast
    • Emissions
    • Fuels
    • Green Shipping
    • Pollution
    • Ship Recycling
    • Technology
  • Smart
    • Connectivity
    • Cyber Security
    • E-navigation
    • Energy Efficiency
    • Maritime Software
    • Smart
  • Risk
    • CIC
    • Detentions
    • Fines
    • PSC Case Studies
    • PSC Focus
    • Vetting
  • Others
    • Diversity in shipping
    • Maritime Knowledge
    • Offshore
    • Ports
    • Reports
    • Shipping
    • Sustainability
    • Videos
  • Columns
    • Opinions
    • Book Review
    • Career Paths
    • Industry Voices
    • Interviews
    • Maripedia
    • Maritime History
    • Resilience
    • Seafarers Stories
    • SeaSense
    • Wellness Corner
  • SAFETY4SEA Events
  • SAFETY4SEA Plus Subscription

© 2021 SAFETY4SEA

This website uses cookies. By continuing to use this website you are giving consent to cookies being used. Visit our Disclaimer.