Interactive SAC and RMV calculator. Mode one computes consumption from a logged dive. Mode two projects gas requirements for a planned dive.
TL;DR.
Pick a tank, enter your dive log, and you'll see your SAC (pressure per minute, tank-specific) and RMV (volume per minute, tank-independent). Switch to "Project" to plan the gas you'll need on the next dive.
1Log a dive — what was your consumption?
Common rec/tech tanks. Choose Custom to enter your own.
Metric: water volume (e.g., 12 for a 12 L tank). Imperial: rated capacity in cuft, plus rated pressure below.
Use the average depth your computer reports — not max depth.
SAC
—
pressure consumed per minute, normalised to the surface
RMV
—
volume of gas you breathe per minute at the surface
Gas used
—
total volume consumed during the dive
Avg ambient
—
ambient pressure used in the calculation (bar)
Where this RMV sits — L/min
Excellent
≤12 L/min Good
12–18 Typical
18–22 High
22–28 Very high
>28
≤12 L/min Good
12–18 Typical
18–22 High
22–28 Very high
>28
Bands are rule-of-thumb planning ranges, not hard cutoffs — individual baseline depends on conditioning, depth, workload, gas, and thermal stress. Tech and cold-water diving routinely run higher.
2Project a dive — how much gas will you need?
Each row: tank type and fill pressure. Total available gas is the sum across all tanks. Per-tank consumption assumes balanced sidemount diving — equal draw from each cylinder.
Will pull whatever RMV the logged-dive panel currently shows.
The pressure each cylinder should still hold at the end of the dive. Common rec convention is 50 bar / 700 psi. Tech / cave plans use larger or rule-based reserves (rule of thirds, rock-bottom).
Gas needed
—
total volume to complete the dive
Total available
—
summed across all cylinders at fill pressure
Pressure consumed
—
drawdown per cylinder · balanced consumption assumed
Required start
—
consumed + reserve, per cylinder
Enter a plan to see whether a single fill is enough.
Quick reference — gas need at common depth × time
Total gas required for the planning RMV above, at common avg depth × bottom time combinations. Add your reserve to convert to a required start pressure.
| Avg depth | 20 min | 30 min | 40 min | 50 min | 60 min |
|---|
Sources & method
- Formula (SAC). SAC = (Pstart − Pend) ÷ (time × Pamb,avg). Standard across PADI, TDI/SDI, GUE, NAUI, and SSI training material — see e.g., PADI Open Water Manual (2024) and PADI Tec Deep Diver Manual (gas planning section). Public-domain arithmetic.
- Formula (RMV). Metric: RMVL/min = SACbar/min × tank water volume (L). Imperial: RMVcuft/min = SACpsi/min × (tank rated cuft ÷ rated psi). Same formula, two unit conventions.
- Ambient pressure. Pamb (bar) = depth ÷ 10 m + 1 (metric) or depth ÷ 33 ft + 1 (imperial). Standard hydrostatic approximation used across all dive-planning literature; see PADI/DSAT Diver Manual: Dive Theory (2009), p. 1-3 — Boyle's law as it applies to diving. Strictly, 1 ata ≈ 1.013 bar; the ÷10 simplification used here matches modern dive-computer convention and the difference is well below the rounding noise of dive planning.
- Tank specifications. Aluminium tank capacities: Luxfer published spec sheets (AL63, AL80). Steel tank capacities: Faber and PST published spec sheets (LP85, LP95, HP100, HP120). Twin-12 L derived as 2 × 12 L water volume.
- Consumption bands. Illustrative planning ranges synthesised from Powell (Deco for Divers, ch. 8 — gas planning), Jablonski (The Six Skills — DIR Min Gas), and DAN annual diving reports. Not hard scientific cutoffs — individuals vary widely. Marked as planning aids, not standards.
- What this tool does not do. No deco-stop gas (this is bottom-gas planning). No rock-bottom / minimum-gas calc (covered in a later S1/S2 tool). No CCR loop modelling.
Educational use only. This tool is not a substitute for certified instruction, supervised training, or a verified dive computer / desktop deco software. Always plan dives within the limits of your training and certification, and consult an active instructor or qualified mentor before applying these concepts in-water. The authors assume no liability for misuse.