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Gas Density

The Gas Density calculator computes the density of your breathing mix at depth and tells you when it exceeds the safety thresholds recognized by the modern technical-diving community. Dense gas raises the work of breathing and CO₂ retention, both of which compound inert-gas narcosis — making density one of the hardest physiological limits in deep diving.

Free Tool

The Gas Density calculator is free for all users with no usage limits.

Inputs​

The page has two independent sections that share the same Dive Parameters card:

  • Altitude and water type (fresh/salt) — affect ambient pressure at depth
  • Depth — only used by the "Gas Density at Depth" section
  • O₂ % and He % — the composition of your breathing mix (N₂ is implicit: 100 − O₂ − He)
  • Target density — only used by the "Max Operating Depth" section (defaults to the 5.2 g/L recommended limit, with a one-click preset for the 6.2 g/L hard cap)

Calculation​

The calculator uses the ideal gas law:

ρ = (P · M) / (R · T)
  • P — absolute pressure in pascals, derived from depth (P_abs = depth × water_density + surface_pressure)
  • M — molar mass of the mix in kg/mol, weighted by fractions: M = fO₂ · 32 + fHe · 4 + fN₂ · 28
  • R — universal gas constant, 8.314 J/(mol·K)
  • T — gas temperature, fixed at 293.15 K (20 °C) as per Anthony 2018 / DAN convention

The result is expressed in grams per litre (equivalent to kg/m³ at these magnitudes).

Two modes​

  • Gas Density at Depth — given depth and a mix, returns the density in g/L at that depth, the absolute pressure, and the surface density of the same mix for reference
  • Max Operating Depth (Density) — inverts the formula: given a target density and a mix, returns the maximum depth at which that target is reached

Recommended limits (Anthony 2018 / DAN)​

The result card is colored according to the safety thresholds:

  • ≤ 5.2 g/L (green) — recommended limit. Minimal CO₂ retention risk
  • 5.2 – 6.2 g/L (orange) — caution zone. Work of breathing increases and CO₂ starts to accumulate
  • > 6.2 g/L (red) — not recommended. Divers approach the limits of pulmonary mechanics and risk severe CO₂ retention

For reference, plain air reaches the 5.2 g/L limit at approximately 39 m of salt water and the 6.2 g/L hard cap at approximately 48 m. Beyond those depths, helium becomes essentially mandatory.

Results​

For the Gas Density at Depth mode, the card shows three numbers:

  • Density at depth (g/L) — colored by severity
  • Absolute pressure (bar) — pressure at the entered depth
  • Surface density (g/L) — for comparison; this is what the same mix weighs at 1 bar

For the Max Operating Depth mode, the card shows:

  • Maximum depth — in meters and feet
  • Absolute pressure (bar) — the pressure that corresponds to that depth
important

The thresholds are physiological guidelines, not hard regulatory limits. Individual susceptibility to CO₂ retention varies. Treat the 5.2 g/L value as the planning maximum for any dive where retention would carry serious consequences (depth, overhead, deco obligation).