Capacity planning is the process of determining a company's production capacity needs to meet changing product demand. It is divided into long, medium, and short term capacity. Long term capacity considers design and trend capacity, medium term is 2-3 years, and short term is daily to quarterly. Effective capacity planning depends on factors like facilities, technology, scheduling, and resources. It allows companies to match production to demand levels, minimizing waste and inventory costs while earning more profits through new product development.