Visibility is usually defined in which unit?

Visibility in diving contexts is most commonly defined in feet, as this unit is widely used in the United States and by various recreational diving organizations. When divers refer to visibility in feet, they are indicating how far they can see clearly underwater, which is crucial for safe navigation and observing marine life.

Using feet as a unit is intuitive for many divers who frequently work in environments where depth and distance are measured in this unit. It allows for easier communication among divers, as the measurement aligns with common practices in diving training and education in many regions.

While other units like meters are also used internationally, particularly in metric systems, the choice of feet is prevalent in many diving discussions, particularly within the context of regions influenced by U.S. diving standards. Other units, such as yards and millimeters, are not typically employed when talking about underwater visibility because they may not provide the same straightforward and practical indication of distance underwater compared to feet.