Minimum gas from 30 m
Turn Pressure — dive planner & gas calculator
Two divers sharing one supply from 30 m need enough gas to reach the surface with a safety stop. How much depends on the cylinder and on how hard the team breathes — the pressure answer is not one number.
The figures
- SCR 15 L/min (the app's Light tier) — 40 bar* from a 15-litre steel, 46 bar from an aluminium 80.
- SCR 20 L/min (Typical — the default a diver gets on "Skip for now") — 45 bar from a 15-litre steel, 61 bar from an aluminium 80.
- SCR 27 L/min (Heavy) — 61 bar from a 15-litre steel, 82 bar from an aluminium 80.
*40 bar is the app's floor — the arithmetic alone gives 33.7. Minimum gas never prints below it, whatever the SCR.
Same depth, same two divers, same ascent: a heavier breather needs more, and the aluminium 80 needs more bar than the 15-litre steel at every tier, because the smaller cylinder holds less gas per bar. At the Typical rate the steel cylinder needs less than the 50 bar habit and the aluminium 80 needs more — the habit is not conservative for every cylinder, which is the point the app was built to make.
Inputs used
- Depth: 30 m
- Ascent style: NDL with safety stop (9 m/min to 5 m, 3 minutes at 5 m, then to the surface)
- Cylinders: single 15-litre steel (232 bar) and single aluminium 80 / 11.1-litre (207 bar)
- SCR: 15, 20 and 27 L/min — the app's Light, Typical and Heavy tiers
- Two divers sharing one supply, at the reserve's own ascent rate
Minimum gas does not depend on your gas strategy (thirds, halves or all-usable) — it is sized for an out-of-gas emergency, not for how you plan to use the rest of the cylinder. It does depend on your SCR, and on conditions such as a current that raise it. Open Turn Pressure, set the depth to 30 m, pick a cylinder and an SCR of 20 L/min, and the app prints the Typical row above.
Source: the app's own pinned test suite for the figures it is sold on
(PublishedReserveFiguresTests.thirtyMetres), matching the corrected 30 m
figures in the App Store description.
Your training, your gauge and your computer decide the dive. This is pre-dive arithmetic, not a dive computer, and it does not make any dive safe.