Why is the capacity of air conditioning units commonly expressed in tons?

The capacity of air conditioning units is commonly expressed in tons because it relates to historical cooling methods that utilized tons of ice. This system of measurement originates from the amount of heat required to melt one ton of ice over a 24-hour period, which is equivalent to 12,000 British Thermal Units (BTUs). This historical reference provides a practical way to quantify cooling capacity. When engineers and manufacturers expressed air conditioning capacity in terms of tons, they were drawing a connection to a widely understood and familiar cooling method, making it easier for consumers and professionals to understand the cooling potential of newer technologies. As air conditioning systems evolved, this tonnage measurement persisted as a standard in the industry.