Ballast is a weight, usually of rubber, or sand, used in an aircraft or ship to attain the desired balance when the center of gravity is not within limits or is not at the location selected by the operator. It is usually located as far aft or as far forward as possible to bring the CG within limits while using a minimum amount of weight. Ballast can also be used to adjust the balance of an aircraft during flight or after landing. For example, if an airplane is overweight and has an undesirable weight distribution, the ballast can be moved and positioned to correct the problem.

In most cases, a ballast is removable. In the context of aviation, ballast is used to meet certain loading conditions that may vary over time. Temporary ballast typically is easy to move around and can have a handle. This type of ballast should be clearly labeled with a weight. The baggage compartment is usually the most convenient location for temporary ballast, as it can be easily accessed and moved around as needed. Ballast is an important part of many aircraft, and it is essential to carefully consider its placement and removal to maintain a safe and balanced aircraft.

Ballast is also used in racing cars to adjust weight distribution and improve handling. In some cases, such as hot air balloons and gliders, ballast is released to ascend and then regained to descend. Finally, ballast can be used simply as a counterweight on cranes and other lifting devices. weight distribution