ton (plural tons) 1  A unit of weight (mass) equal to 2240 pounds (a long ton) or 2000 pounds (a short ton) or 1000 kilograms (a metric ton). 2  A unit of volume; register ton. In refrigeration and air conditioning, a unit of thermal power defined as 12,000 BTU/h (about 3.514 kW or 3024 kcal/h), originally the rate of cooling provided by uniform isothermal melting of one short ton of ice per day at 32 °F (0 °C). (colloquial, hyperbolic) A large amount.