Scuba Gas Volume at Depth Calculator (Boyle Law)
Calculate compressed gas volume at depth using Boyle Law.
Enter surface volume and depth to see how much your air shrinks at 30, 60, or 100 feet underwater.
Boyle’s Law and Diving
Boyle’s Law states that for a fixed temperature, gas volume is inversely proportional to absolute pressure: P₁ × V₁ = P₂ × V₂
In diving, depth determines pressure. Each 33 feet (10 m) of seawater adds 1 atmosphere to ambient pressure.
Pressure at depth:
| Depth | Absolute Pressure |
|---|---|
| Surface | 1 ATA |
| 33 ft (10 m) | 2 ATA |
| 66 ft (20 m) | 3 ATA |
| 99 ft (30 m) | 4 ATA |
| 132 ft (40 m) | 5 ATA |
| 165 ft (50 m) | 6 ATA |
Practical implications for divers:
1. Air consumption multiplies with depth: A breath at 33 ft uses 2× the surface gas. At 99 ft, you’re consuming 4× the surface volume per breath. This is why deep dives end on gas, not on time.
2. BCD and drysuit volume changes: Air added at depth must be vented during ascent — or expanding gas overinflates and rockets you to the surface (squeeze and reverse-block also occur in reverse on descent).
3. Lung over-expansion: Holding breath while ascending is the #1 cause of fatal diving injuries. A lung-full at 33 ft doubles in volume by the surface — exceeding lung capacity in seconds.
4. Buoyancy compensator pre-dive air: Air added at the surface compresses to half-volume by 33 ft. Divers compensate by adding more air during descent.
5. Gas planning rule of thirds: For non-deco recreational dives, plan gas as: 1/3 outbound, 1/3 return, 1/3 reserve. Depth multiplies real-world gas consumption — a 4 ATA dive uses 4× the SAC rate volume.
The volume at depth formula: V_depth = V_surface / (depth in ft / 33 + 1)
So 12 cubic feet of air on the surface becomes 4 cubic feet at 99 ft (4 ATA).