The ton of refrigeration dates from the days when ice was the main way to keep things cold. Melting a short ton (2,000 lb) of ice over a day absorbs about 12,000 BTU every hour, so that became the unit. It is still everywhere in India: an air conditioner is described as 1.5 ton, and cold-room and chiller plant capacity is quoted in TR.
Plug-in commercial cabinets are much smaller, usually a fraction of a ton. That is why their compressors are often described in horsepower fractions instead, such as a quarter or half HP. Horsepower describes motor size, not cooling output, and the same horsepower compressor gives very different cooling capacity at chiller and freezer temperatures.
For walk-in cold rooms and central systems, tonnage is calculated from a proper heat load. Guessing tonnage from floor area or copying a neighbour's system often leads to a room that cannot pull down a warm delivery in May or June.