Let understand about GRT & NRT

Gross registered tonnage is also called GRT or GT.

• We can get a doubt that why we measuring in tonnes?

Here we actually measure the volume and not the weight.

• Why it's called RT?

According to the 1967 tonnage rule 

1RT = 100 cubic feet.

So if we have 20 no of cargo spaces with 100 cubic feet.

Then,

20*100cubic feet = 2000cubic feet.

= 20RT.

• Anything on the ship is enclosed and normal shape which can be enclosed is measured as gross registered tonnage.
• The including everything like cargo holds, engine room, steering room, cofferdam, etc.

Net registered tonnage is called NRT or NT.

The measuring of Only the cargo carrying capacity on a ship is called NRT.