There are 3.517 kilowatts in a ton of refrigeration, so in order to convert kW to tons, divide the number of kW by 3.517. One ton of refrigeration is approximately 12,000 BTUs, or British thermal units, which is the rating system of air conditioning units in many English-speaking countries outside of the United States.
The units of refrigeration come from the industry of making ice. Originally, manufacturers of ice needed an easy to understand system that related to the production of ice. A ton of refrigeration is the capacity needed in order to freeze a short ton (0.907 long tons) of water to zero degrees within 24 hours. There is also a tonne, rather than a ton, of refrigeration, and a tonne of refrigeration is the capacity needed to freeze a metric ton, or 1,000kg, to 0 degrees Fahrenheit within 24 hours. A tonne of refrigeration is equal to 3.861 kW.
Most air conditioning units for a house are rated between 1 ton and 5 tons, the equivalent of 3.5 to 17.5 kW or 12,000 to 60,000 BTUs per hour. Large chiller systems, such as those for industries, can be found ranging up to 800 tons of refrigeration, the equivalent of 2.8 million kW or 9.6 million BTUs per hour.