Nominal tonnage in air conditioning capacity refers to the manufacturer’s stated or nameplate capacity, typically measured under specific, standardized laboratory conditions for uniform comparison. This is the figure you’ll find on the unit’s specifications and the one used for marketing purposes. Actual tonnage, on the other hand, reflects the AC unit’s real-world performance based on actual operating conditions and factors in your home. These real-world conditions, such as varying indoor and outdoor temperatures, humidity levels, and airflow, can cause the actual capacity to be lower than the nominal rating. For instance, higher outdoor temperatures might lead to a 3-ton unit having an actual capacity of 2.8 tons when installed in your home. It is important to note that the term “ton” in this context refers to the amount of heat removed, not the physical weight of the unit. This unit of measurement originated from the amount of heat required to melt one ton of ice in 24 hours.