Rock Bottom Gas Calculator (Minimum Gas for Scuba Diving)

How to Use This Rock Bottom Gas Calculator

This tool estimates the minimum reserve gas (rock bottom) required for two divers to safely ascend from a planned depth in an out-of-gas emergency, including the ascent and a safety stop.

It is a simplified training and planning aid only — not a replacement for proper training, dive planning procedures, or instructor guidance.

You will need:

  • Your planned depth
  • Your emergency RMV (per diver, at the surface)
  • Your ascent rate
  • Your safety stop time
  • Your cylinder size (internal volume in litres)

Tip: For emergency planning, many divers use a higher RMV than normal (for example 25–35 L/min per diver) to account for stress and workload.

Steps:

  1. Enter your planned depth (metres or feet)
  2. Enter your RMV per diver
  3. Set your ascent rate and safety stop time
  4. Enter your cylinder size (e.g. 12 L steel, 15 L steel)
  5. Click Calculate Rock Bottom

The calculator will show:

  • The minimum gas required (litres)
  • The equivalent reserve pressure (bar)

Important: This reserve is the absolute minimum gas you should have before leaving the bottom.
Always round up and add extra margin. Your instructor’s procedures and your dive plan take priority.

Rock Bottom Gas Calculator (Minimum Gas for Scuba Diving)

This tool estimates the minimum gas (rock bottom) required for two divers to safely ascend from depth in an out-of-gas emergency. It includes ascent time and a safety stop. This is for educational planning only.

Safety note: This does not replace training, proper gas planning, or a dive computer. Always follow your training and agency standards.

Inputs

L/min
m/min
minutes
litres

Your Result

Minimum Gas Required:

—

Equivalent Tank Pressure:

—

This is the minimum gas you must keep in reserve before leaving the bottom.

Important Notes

  • This assumes two divers breathing from one supply.
  • Uses a constant elevated breathing rate for the entire ascent.
  • Does not include decompression obligations.
  • Always round up and add extra margin.

Rock Bottom Planning Tips

Rock bottom gas is about surviving the worst-case scenario, not maximizing bottom time.

🤝 Plan for two divers, not one

Rock bottom assumes you and your buddy are both breathing from the same cylinder during the ascent. Never plan reserves for only yourself.

📈 Use a conservative RMV

Stress, current, cold, and task loading increase breathing rate. Use a higher, realistic RMV for emergency planning.

⬆️ Always round up and add margin

Never use the exact number shown. Round up the reserve pressure and add extra buffer gas.

🧭 Deeper dives need bigger reserves

As depth increases, gas use during ascent increases rapidly. Deep dives require significantly larger reserves.

❄️ Add extra margin in difficult conditions

Cold water, strong current, poor visibility, or overhead environments all require larger reserves.

🖥️ Follow your training and dive computer

This tool does not replace proper gas planning procedures taught in training or your dive computer’s guidance.

Good gas planning is not about staying longer — it’s about being able to deal with problems calmly and safely.

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