What is the minimum height a child must be to stop using a booster seat?

The minimum height a child must reach to stop using a booster seat is 4 feet 9 inches. This height requirement ensures that the vehicle's seat belts fit properly across a child's body, specifically across the upper thighs and the shoulder, not on the neck or stomach, which can cause serious injury in the event of an accident.

Using a booster seat is vital for proper seat belt positioning; without it, younger or smaller children may not be adequately protected by standard seat belts. The specified height of 4 feet 9 inches is based on safety research that indicates this is a point at which most children will be able to safely use an adult seat belt, effectively reducing the risk of injury in a collision.