Maximum Depth

The deepest point reached during a dive, and in planning, the depth limit that sets no-decompression time, gas needs, and certification bounds.

Maximum depth is the deepest point of a dive, and in planning it is the number everything else hangs on. It sets your no-decompression limit, your gas consumption rate, the intensity of nitrogen narcosis, and for nitrox divers whether the mix stays within its maximum operating depth. Agencies attach depth limits to training levels: typically 18 m for a newly certified open water diver, 30 m with advanced training, and 40 m as the general boundary of recreational diving.

The planned maximum depth is agreed before the dive and treated as a hard floor, not a suggestion, because the plan's gas and time math assumed it. Your dive computer records the actual maximum reached, which is the figure that goes in the logbook, and it is often a little deeper than intended: a moment chasing a photo down a drop-off is all it takes. Building in a small buffer between planned depth and any hard limit is standard practice.

Depth also compounds other factors. At 40 m you breathe roughly five times the gas per minute that you do at the surface, narcosis is meaningful on air, and the surface is a long, controlled ascent away. Respecting maximum depth is less about the number and more about everything that scales with it. Plan for it deliberately and the number takes care of itself.