Scuba Gas Planning Basics: RMV, Reserve, MOD, Nitrox

Gas planning is one of the most important skills in recreational diving—and one of the most overlooked. Computers make it easy to forget that you’re responsible for your own air. But good planning doesn’t just help you avoid running low. It also gives you the flexibility to handle problems calmly, extend your dive time, and support your buddy.

This section introduces the fundamentals of gas planning and connects you to both the concepts and the tools that make it practical.

Topics Covered

RMV vs SAC

SAC is easy to calculate but limited to one tank. RMV measures your true gas use in volume, making it essential for real dive planning. If you want to calculate reserves, run time, or switch tanks, RMV is what matters.

Calculating Minimum Reserve

Minimum Reserve Gas ensures you and your buddy can safely ascend from depth in an emergency. Using the CAT formula, it calculates the volume needed—not including a safety stop—and can be translated into PSI for your specific tank. Always round up for safety and clarity.

Recreational Gas Planning

Recreational gas planning means more than checking your tank. It includes calculating your reserve, understanding turn pressure, and choosing the right gas strategy for your dive conditions. With just a few numbers, you can dive safer and smarter every time.

Using Nitrox

Nitrox reduces nitrogen absorption, which helps extend no-decompression limits and shorten surface intervals. It requires proper analysis, tank labeling, and setting your dive computer correctly. If available and within depth limits, Nitrox is a smart choice for most dives.

Calculating MOD

Maximum Operating Depth (MOD) tells you how deep you can safely dive a nitrox mix without exceeding oxygen limits. Understanding how to calculate MOD using Dalton’s Triangle gives you control over gas planning, beyond relying on your dive computer alone.

Calculating EAD

Equivalent Air Depth (EAD) shows how much less nitrogen you're absorbing with Nitrox by comparing it to an air dive at a shallower depth. While modern computers handle this automatically, understanding EAD helps explain why Nitrox extends no-decompression time.