The ton of refrigeration dates from the days when ice was produced commercially: the heat needed to melt 2,000 pounds (907 kg) of ice at 0 °C in 24 hours. That equals 12,000 BTU/h or 3.517 kW. It is still common in chiller, air-handling unit and imported equipment catalogs; a "100-ton chiller" means 352 kW of cooling capacity.
In cold store and industrial refrigeration catalogs the European unit, kW, is the standard. For conversion, 1 TR = 3.517 kW and 1 kW = 0.284 TR; the rule of thumb is "divide kW by 3.5". When comparing a quotation given in tons with one given in kW this conversion must be made; otherwise a difference of nearly threefold goes unnoticed.
Tons of refrigeration should not be confused with product tonnage. "A 10-tonne apple store" describes the weight of the product, and the cooling capacity that store needs cannot be known without a calculation; 10 tonnes of apples may need 3–8 kW depending on the daily intake and the room. The unit converter gives the conversions between kW, kcal/h, BTU/h and TR as a ready table.