Calculating GRT for Mariner Credentials


I have a question about Gross Registered Tonnage for Mariner Licensing. A good portion of my sea time is on a private yacht that just shows Gross Tonnage on the COI, not Gross Registered Tonnage. Is there a formula used to determine Gross Registered Tonnage for a vessel for Mariner Credentials? Thanks in advance,


The USCG considers 1600 GRT equal to 3000 GT.

I’m not sure what they do about smaller vessels.

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Here is what I have used for CG 719S Sea Service Form.

A simplified set of gross tonnage formulas is set forth by the U.S. Coast Guard Marine Safety Center, which are based on three measurements: Length (L), breadth (D), and depth (D). Under this system, the means of estimating gross tonnage is as follows:

For power boats: Gross Tonnage = (. 67 x L x B x D) / 100.

For a sailing boat with keel, Gross Tonnage = (.375 * L * B * D) / 100

For freighters with angled or cylindrical hulls, Gross Tonnage = (.67 * L * B * D) / 100

For ships with square barge-shaped hulls, Gross Tonnage = (.84 * L * B * D) / 100**

For a boat with a simple sailing hull, Gross Tonnage (GT) = (.5 x L x B x D) / 100**

Vessel Gross Tonnage Calculator

And 500 GT = 200 GRT. See also 46 CFR 11.211(h).


Where does it state you can use these formulas to calculate Gross Registered Tonnage for the CG 719S?


You’re making this harder than it needs to be. If the vessel is only measured in GT you don’t need GRT See the link I posted above.

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Thank you again. I like idea to simplify and not complicate the issue.

However, I have for years used 46 CFR 69.209 and the Simplified Measurement Tonnage Guide 1 for my calculations for the 719S form.

Many years ago, I was referred to the Gross Register Tonnage regulation of small vessel calculations if it was unknown.

Thanks for all of the great information. So if I am working an a vessel that’s only calculated with the simplified tonnage, how does this type of Vessel Gross Tonnage work when looking to upgrade your license when the Sea Service for the vessels needs to be in Gross Registered Tonnage? I attached a picture of the specs on the vessel along with a license checkoff list. Thanks for all of your help.


I like Mr Cavo’s method.

If this is for other purposes then I would use the vessel’s name and enter the
CGMIX Coast Guard Port State Information Exchange

Last resort: Vessel Gross Tonnage Calculator or by formula 46 CFR 12.603.

77.8’ x 20.7’ x 10.3’ x .67/100 = 111.14 tons

Thanks for the information. Would the 137 Gross Tons vessel I work on satisfy a Sea Service requirement that’s calling for time on vessels of 100 GRT or more? Thanks again.


This boat I work on is US Flagged.

I recommend looking at the GRT vs gt, Professional Mariner Forum Dec 2013 thread and Mr. Cavo’s post regarding the relationship between the two.

Thanks for the information jdcalvo. What is the National Maritime Center going to consider a 137 Gross Tonnage vessel to be for Gross Registered Tons?


Looking at the CG-719S form, it asks to list “Vessel Gross Tons”. I will put the 137 Gross Tons and will see what happens. See attached.

Seems that following Cavo’s guidance we both found our solution.


The formulas I provided earlier were based on both the CFR and Simplified Measurement Gross Tonnage Guide to comply with the guidance for filling out the 719S form found in Documenting Sea Service on the NMC website. Based on my reading NMC is calculating Gross Tons as GRT. I believe that they will calculate for you given the Length, Beam and Draft based on the vessel type.

Let me know how you read the guidance.

Sorry for the run on sentence.

2 posts were split to a new topic: GRT/NRT has been replaced by GT/NT in all international trade since 1982

Your entire comment is completely irrelevant and off topic.