Cooling load is the rate at which heat must be removed from a conditioned space to maintain the desired indoor temperature on the hottest expected day. Like heating load, it is measured in BTU per hour (or tons) and is calculated using ACCA Manual J.
Cooling load has more variables than heating load. In addition to heat conducted through the building envelope, cooling load includes: solar heat gain through windows (varies by orientation and shading), internal heat gains from occupants (each person generates about 250 BTU/hr), lighting, appliances and computers, latent load (moisture removal), and ventilation load.
Cooling loads are often higher on the south and west sides of buildings due to afternoon sun exposure. This is why zoning systems and window treatments can significantly reduce cooling costs. Proper Manual J cooling calculations prevent the epidemic of oversized air conditioners that fail to adequately dehumidify because they short-cycle.