How the calculation works
A cooling rating in BTU per hour converts to watts with the same factor as heat output, used in reverse:
- watts = BTU/hr ÷ 3.41214
- tons of cooling = BTU/hr ÷ 12,000
One watt is 3.412142 BTU/hr (International Table BTU, per NIST Special Publication 811); the calculator uses 3.41214, and the common rounding 3.412 changes results by less than 0.01%. One ton of refrigeration is 12,000 BTU/hr by definition.
The result is the IT load whose heat output equals that cooling capacity, assuming the equipment’s electrical power all becomes heat. It does not include other heat in the room (lighting, people, the building) or any redundancy, and it is not the power the cooling unit itself uses.
Worked example
A server room has a 24,000 BTU/hr (2-ton) cooling unit:
- watts = 24,000 ÷ 3.41214 = 7,033.7 W, or 7.03 kW
- tons = 24,000 ÷ 12,000 = 2 tons
So the unit’s rated capacity matches about 7 kW of IT load before allowing for other heat sources, its capacity at your room conditions, or a second unit for redundancy.
A 12,000 BTU/hr (1-ton) unit matches 3,516.9 W.
