Tools
Gas Usage
Plan how much breathing gas a dive will use and check that your cylinder holds enough, segment by segment.
Last updated 3 июня 2026 г.
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What it is
The Gas Usage calculator works out how much breathing gas a planned dive will consume and whether the cylinder you packed will get you through it with a reserve to spare. You describe the dive as one or more steps (a depth and a time each), tell it your cylinder and your breathing rate, and it tracks the pressure draining out of the cylinder as the dive runs.
It is a planning tool for the surface. Build the profile before you splash, see where your gas runs low, and adjust depth, time, or cylinder size until the numbers work. In the app this screen is titled Gas Usage.
How to use it
Open Gas Usage
From the Plan tab, open Gas Usage.
Set up your cylinder
In the Cylinder Setup card, choose Single cylinder or Twin Set, then enter the volume and the Start Pressure. The volume field is labelled Volume for a single cylinder and becomes Volume (per cylinder) once you switch to Twin Set, which doubles the volume internally, so you still enter the size of one cylinder. If you have saved gas presets, tap Quick Fill to load one preset’s volume, pressure, and single or twin setting all at once.
Enter your breathing rate
In Add Plan Step, enter your SRMV (surface respiratory minute volume, your breathing rate at the surface in litres or cubic feet per minute). If you do not know it, measure it first with the SAC/SRMV calculator and copy the number across.
Describe the step
Still in Add Plan Step, enter the Depth and the Time for this part of the dive. The card shows the Consumed Gas for the step (the surface-equivalent volume used) and the pressure left in the cylinder beside it, updating as you type.
Save the step and add more
Tap Add to Plan to push the step into your Dive Profile. Adding a step clears the Time field while keeping your depth and SRMV, so you can type the next segment’s duration straight away. Each saved step keeps the SRMV it was entered with, so you can use a higher rate for a working segment and a calmer one for the safety stop.
Read the summary
The Summary footer totals the gas consumed, shows the pressure remaining with a progress bar, and warns you if you drop below your reserve.
Inputs and outputs
Everything follows your unit settings. Depth reads in metres or feet, pressure in bar or psi, and volume and SRMV in litres or cubic feet, all set from the app’s unit toggle.
| Field | Meaning | Notes |
|---|---|---|
| Single cylinder / Twin Set | Cylinder configuration | Twin Set doubles the effective volume |
| Volume | Water volume of one cylinder | Labelled Volume (per cylinder) in Twin Set mode; capped at 30 L (1.06 ft³) |
| Start Pressure | Pressure in the cylinder at the start | Minimum 50 bar (725 psi) |
| SRMV | Your surface breathing rate | Per minute; 5 to 50 L/min (0.18 to 1.77 ft³). Measure it with the SAC/SRMV tool |
| Depth | Depth of the current step | Drives the ambient pressure; 1 to 500 m (3 to 1640 ft) |
| Time | Minutes spent at that depth |
The tool opens pre-filled with sensible defaults: 12.2 L cylinder, 200 bar start pressure, 20 m depth, 20 minutes, and a 20 L/min SRMV. The fields are bounded, so if you type a value outside the ranges above the tool clamps it.
The calculator converts depth to an ambient pressure (about 1 bar of water for every 10 m, set by your Water Density setting), multiplies by your SRMV and the time to get the surface-equivalent litres used, then turns that back into pressure drained from your cylinder. Water Density offers four options (Fresh, EN13319, Salt, or Red Sea), with salt water at the familiar 10 m per bar.
| Output | Meaning |
|---|---|
| Consumed Gas | Surface-equivalent volume (litres or cubic feet) used for the current step, before you save it. The pressure effect shows in the remaining value beside it |
| Dive Profile | Your saved steps, each with its gas used, the gas remaining after it, and the cumulative runtime |
| Summary | Total gas consumed, remaining pressure, a used/remaining progress bar, and a reserve warning |
Reserve and the rule of thirds
The tool does not print a single “turn pressure” number. Instead it compares your remaining gas against a reserve threshold set by your gas reserve rule in Settings, and warns you when you fall below it.
- Rule of thirds keeps a third of your gas in reserve. The warning fires when remaining gas drops below one third of your starting pressure (a 200 bar fill turns around 67 bar). This is the usual choice for overhead and demanding dives.
- Rule of sixths keeps a larger reserve, warning below four sixths of your starting pressure. It is the more conservative option.
- Below 50 bar the tool always raises a critical alert and turns the reserve red, whatever reserve rule you set. That floor overrides the rule threshold, because under 50 bar is too little gas to ascend and surface safely. If the remaining gas reaches zero, the plan fails outright.
Watch the step in your profile where the remaining gas first crosses that threshold: that is the point in the dive where you should already be heading up.
SAC vs SRMV
You enter a breathing rate here. The field is labelled SRMV in the app, and there are two ways divers express a breathing rate.
SRMV (surface respiratory minute volume) is a true volume per minute at the surface, in litres or cubic feet per minute. It belongs to you, not your cylinder, so the same SRMV works whatever cylinder you pick. This is the value Gas Usage asks for.
SAC (surface air consumption) is a pressure drop per minute for one specific cylinder, in bar or psi per minute. It is handy at the fill station but it changes the moment you switch cylinder sizes, so it is not portable between cylinders.
Measure either one from a real dive with the SAC/SRMV calculator, then feed the SRMV into this planner.
Behaviour and limits
- The plan is only as good as the SRMV you give it. Your real breathing rate climbs with cold, current, exertion, and stress, so plan with a rate from a comparable dive, not your calmest ever.
- It models gas for an open-circuit recreational profile. It does not build decompression schedules or auto-switch deco gases. For staged deco dives use the Deco Planner, which estimates gas required per cylinder as part of the schedule.
- Numbers reflect exactly what you typed. Confirm your actual fill pressure and analysis before the dive.
Related
- SAC/SRMV calculator measures the SRMV this planner needs.
- Deco Planner handles gas planning for staged decompression dives.
Parts of this guide were drafted with AI assistance and may contain mistakes. It's educational, not a substitute for training. Always dive within your certification and verify with your instruments.