Online decompression scuba dive planner

Planning a single dive or a repetitive dive? Set the depth, gas mix, and the duration you want. This Online Decompression Scuba Dive Planner works out the NDL, the decompression-stop profile, and the residual nitrogen. Plan your dive safely before you get in the water.

The minutes here come from the SSI Air/EANx metric tables with Doppler limits. Group letters, residual nitrogen, and surface intervals follow that table.

Gas includes an 18 m/min descent, bottom time, a 9 m/min ascent, and a 5-minute safety stop at 5 m when the dive is deeper than 9 m. Each dive starts again from its own start pressure. The surface interval runs from the moment you reach the surface until the next dive starts. Less than 10 minutes still counts as the same dive. More than 12 hours counts as a first dive.

CNS and OTU cover the descent, bottom, ascent, and safety stop at each segment's PPO2. The CNS clock halves every 90 minutes on the surface. OTU adds up across the trip, with no credit during the surface interval. On the nitrogen table, exactly 12 hours usually leaves group A. More than 12 hours clears it.

RG is the group letter. RT is residual nitrogen. BT is bottom time. TT is RT plus BT. On the next dive, BT is the minutes you still have, and TT is RT plus BT. SI is the surface interval. D is depth. A safety stop of 3–5 minutes at 5 m is recommended deeper than 9 m.

What the words mean

Group: A letter for the nitrogen you still carry. A is the least. Later letters mean more nitrogen.
Residual nitrogen: Nitrogen still stored in your body after the dive you just did. The table writes that leftover as minutes already spent at the next dive's depth.
Bottom time: How long you stay at the dive depth, in minutes.
Surface interval: How long you stay on the surface between two dives. Nitrogen leaves during this rest.
PPO2: PPO2 stands for partial pressure of oxygen. It is how hard the oxygen presses on you at that depth. The number rises as you go deeper.
MOD: MOD stands for maximum operating depth. It is the deepest you can go on this mix before the oxygen passes the limit you set.
EAD: EAD stands for equivalent air depth. Nitrox has less nitrogen than air, so the dive is counted as shallower than the depth you actually are.
Gas: An estimate of the litres one diver uses. It comes from the SAC rate and the pressure, for an 18 m/min descent, the bottom time, a 9 m/min ascent, and a 5-minute safety stop at 5 m when the dive is deeper than 9 m.
Reserve: The lowest pressure that should still be in the cylinder when you are back on the surface. If the calculated end pressure is under this number, the plan is marked as a risk.
SAC: SAC stands for Surface Air Consumption, the gas you use per minute at the surface, in litres. At depth, that rate is multiplied by the pressure.
CNS: CNS is the oxygen clock for the nervous system. In this plan it covers the descent, the bottom, the ascent, and the safety stop, then halves every 90 minutes on the surface.
OTU: OTU stands for oxygen toxicity unit, the oxygen dose for the lungs. In this plan the dose adds up across the trip, with no credit during the surface interval.

Group letters, residual nitrogen, and surface intervals follow the SSI Air/EANx metric tables with Doppler limits. Oxygen-clock time follows the NOAA Oxygen Exposure Limits, and OTU follows the OTU rate table. This dive plan is designed solely as a dive planning aid. It is not a substitute for formal training, certification, or the judgment of a dive computer or a guide on site. The decision to dive, and safety underwater, remain each diver's own responsibility. Always plan your dive and dive your plan.