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Rock Bottom

The Rock Bottom calculator determines the minimum gas reserve you need to safely ascend from depth in an emergency. It accounts for problem-solving time, ascent rate, safety stops, and, optionally, sharing air with a buddy.

Premium Feature

The Rock Bottom calculator requires an active premium subscription.

Inputs​

  • Maximum depth: the deepest point of the planned dive
  • Tank volume: cylinder size in liters
  • Personal SAC rate: your Surface Air Consumption rate (in L/min)
  • Ascent rate: how fast you ascend (in m/min or ft/min)
  • Stress factor: a multiplier (2x--3x) applied to your SAC to simulate emergency breathing under stress
  • Safety stop depth and duration: optional; adds gas for a stop during ascent
  • Share air with buddy: toggle that doubles gas consumption to account for two divers breathing from one tank
  • Altitude: elevation of the dive site (affects ambient pressure calculations)
  • Water type: fresh or salt water (affects water density and pressure at depth)

Calculation phases​

The calculator computes gas needed for three phases of an emergency ascent:

  1. Problem-solving time at depth: a fixed period at maximum depth while you identify the problem and prepare to ascend, breathing at the stressed SAC rate
  2. Ascent to safety stop or surface: gas consumed while ascending at the configured ascent rate, with the stress factor applied
  3. Safety stop: if enabled, gas consumed during the safety stop at the specified depth and duration

Each phase uses the stressed SAC rate (your normal SAC multiplied by the stress factor) to represent increased breathing during an emergency situation such as panic, exertion, or air sharing.

Buddy sharing​

When the Share air with buddy toggle is enabled, gas consumption is doubled across all phases. This simulates the worst-case scenario where both you and your buddy must ascend on a single tank after an out-of-air emergency.

Results​

The minimum gas reserve is displayed in two forms: Gas volume (in liters) and Turn pressure (in bar or PSI). The turn pressure is the tank pressure at which you must begin your ascent to ensure you have enough gas for an emergency return to the surface.

The calculator also displays the ascent time: total time from depth to surface, including any safety stop.

important

Rock bottom calculations assume worst-case scenarios. Always plan conservatively and never cut into your reserves during a dive.