The space between a forklift mast and a door depends on the size and type of forklift, as well as the door's height. Generally, it's recommended to have at least 4-6 inches of clearance to allow for safe operation and avoid collisions. Additionally, consider the mast's height and tilt angle when operating in confined spaces. Maintaining adequate clearance is crucial for preventing damage to both the forklift and the door, as well as ensuring smooth and safe maneuverability.