Rock Bottom Calculator

Rock Bottom — Key Features

• Calculate minimum gas for emergency ascent from any depth
• Configurable stress factors (2×, 2.5×, 3× SAC)
• Account for buddy air sharing during emergency
• Include safety stop gas consumption
• Get your recommended turn pressure
• Support for custom ascent rates and stop profiles

Rock Bottom — How It Works

Enter your maximum depth, cylinder size, SAC rate, and stress multiplier. The calculator builds an emergency ascent profile from depth back to the surface — including a stressed buddy share at depth, a controlled ascent with stops, and a safety stop — then totals the gas required and converts the total into a turn pressure for your cylinder. Rock Bottom answers a single question: what is the minimum pressure I can be at when something goes wrong, and still get both divers up alive? It is not a panic margin — it is the floor under every other gas-planning number. The stress factor (typically ×1.5 to ×2 over baseline SAC) reflects the elevated breathing rate of a real out-of-gas event, where heart rate spikes and tidal volume drops. Recalculate Rock Bottom whenever depth, team size, cylinder, or SAC changes — never reuse yesterday's number on today's dive. Begin your return when pressure hits the calculated turn-pressure, regardless of where the plan said you would be at that moment.

Why Calculate Rock Bottom?

• Never run low on gas in an emergency situation
• Know exactly when to turn your dive around
• Account for worst-case stress and buddy sharing
• Essential safety practice for all divers

Rock Bottom — Frequently Asked Questions

What is rock bottom?

Rock Bottom is the minimum cylinder pressure at which you can still complete a safe emergency ascent for two divers — including a stressed buddy share at depth, controlled ascent with stops, and safety stop — without running out of gas. It is the floor under every other gas-planning number. When your pressure reaches Rock Bottom, you turn the dive and head up, regardless of where the plan said you would be at that moment. The number is recalculated for every dive based on depth, cylinder, SAC, and stress assumption.

What stress factor should I use?

A stress multiplier of ×1.5 to ×2 over your baseline SAC is standard for Rock Bottom because a real out-of-gas event spikes the heart rate, drops tidal volume, and increases minute ventilation dramatically. GUE and most technical agencies use ×2 for both divers as a conservative default; some rec-tech agencies use ×1.5. Use ×2 when diving with new buddies, in cold water, in current, or any time judgement could be impaired. Use ×1.5 only when sharing with a known calm partner in benign conditions.

Should I include buddy sharing?

Yes — Rock Bottom is fundamentally a buddy-share number, computed for two divers breathing from your cylinder during the worst-case ascent. Solo or single-tank dives use a different reserve (typically a third of the tank for turn pressure, plus an absolute minimum at surface). For team diving the assumption is that your buddy is the one who runs out, and you donate your long-hose primary while ascending together. If you dive solo, recalculate using single-diver gas with redundant cylinder reserves instead.

How is rock bottom calculated?

Rock Bottom = (SAC × stress × ascent time × average ascent depth) + (SAC × stress × stops time × stop depth) for two divers. The planner builds an ascent profile from your maximum depth: stressed buddy share at depth for 1 minute, controlled ascent at 9 m/min with deep stops if appropriate, normal ascent above 20 m, and a 3-minute safety stop at 5 m. Each phase's gas is summed and converted back to cylinder pressure using cylinder volume. The total is the minimum you must keep in reserve at any point in the dive.

Does rock bottom change with depth?

Yes — deeper dives require more Rock Bottom because the emergency ascent takes longer and the average ambient pressure during ascent is higher (more gas consumed per minute). Doubling depth roughly triples Rock Bottom: a 20 m dive may need 30 bar reserve on a 12 L cylinder, while a 40 m dive needs closer to 90 bar. This is one reason deep dives feel pressure-limited even with the same cylinder — much of your gas is locked into the reserve and unavailable for bottom time.

Should I include a safety stop in my rock bottom?

Yes — the safety stop is included in Rock Bottom because it is a planned part of the ascent and consumes real gas. A 3-minute stop at 5 m for two stressed divers on a 30 L/min combined SAC uses about 50 litres of gas, which is significant on a small cylinder. The planner includes it by default for any dive deeper than 10 m. You can disable it for short, shallow dives where it adds no value, but for typical recreational and technical profiles the safety stop should always be part of the gas plan.

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