The register ton is a unit of volume in the shipping world and uses the symbol GRT.
1 register ton is equal to 100 ft³ or 2.832 m³.
The register ton is used in shipping to measure the amount of cargo on a vessel. The phrase is often mistaken for a unit of mass or weight because of the term 'ton' but should not be confused.
The cubic metre (or cubic meter; US spelling) is a unit of volume and is derived from an SI unit with the symbol m³.
1 cubic metre is exactly 1000 litres. It is also ≈ 6.29 barrels, ≈ 220 imperial gallons and ≈ 35.3 cubic feet.
1 cubic metre of water in normal conditions (≈4 °C) weighs exactly 1000 kg (or 1 tonne).)
The cubic metre is the unit used to measure water usage and often water bills are broken down into how many m³ has passed through the property / business.