Turn Pressure
Dive planner & gas calculator for iPhone
Free. iPhone, iOS 17 and later. No account, no ads, no analytics.
Most recreational divers were taught one number: surface on 50 bar, no matter the depth, the cylinder, or who they're diving with. It's not that nobody plans — it's that the plan never changes with the dive.
Turn Pressure runs the actual numbers instead. Tell it how deep you're going, what cylinder you're carrying and who's breathing it, and it gives you a turn pressure, the minimum gas to get two divers up from the deepest point, an NDL or bottom-time limit, and how long you can stay at maximum depth — before you kit up.
What it does
- Minimum gas that scales with your cylinder and your SCR — at a Typical 20 L/min, the same ascent from 30 m needs 45 bar out of a 15-litre steel and 61 bar out of an aluminium 80. Not a flat reserve.
- Turn pressure on thirds, halves or all-usable gas.
- NDL / bottom-time limit from Bühlmann ZH-L16C, for air and every nitrox mix (EAN28, EAN32, EAN36), with gradient-factor presets from 15/85 and 30/70 to 100/100, defaulting to 45/95, so you can match your dive computer.
- An ascent you can brief — a ladder of levels, each a depth to hold or be shallower than, drawn and labelled on the chart, at an ascent rate you choose from 3 to 9 m/min.
- Time at maximum depth, set on a slider up to the most your gas and your NDL allow — and when the NDL caps the deep part of the dive, the plan spends what's left on the way up instead of sending you up with a full-looking gauge.
- Repeat dives that use the dive you actually did — the depth and time you enter, run back through the same tissue model, not a flat percentage knocked off the limit.
- Your own SAC rate, typed, worked out from one real dive, or started from a tier — kept as a dated list with a trend chart.
- A dive log — sites, conditions, notes, photos and buddies present, because it's what your SAC rate and your repeat-dive question are built on.
- Metric and imperial, in the numbers each is actually dived in — 100 ft and AL80, not 98 ft and "81 cu ft".
- Saved briefs for the dives you run over and over.
What it does not do
No account. No ads. No analytics. Your divers and briefs sync only through your own iCloud, and the rest stays on your phone. It's a no-stop, recreational planner: it doesn't plan decompression dives, stage gases or bailout, and it isn't meant to run during the dive — plan with it on the boat or the night before, then go by your gauge and your computer in the water.
Your training comes first. In the water, go by your pressure gauge and your computer. This app helps with the arithmetic and accepts no liability for any dive.
Worked examples
Real figures from the app, for dives divers actually ask about: