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Dissimilar Tank Volume Gas Matching

When buddies have different-sized tanks, calculating a turn point by pressure alone (e.g. "rule of thirds") gives one diver more gas than the other — and can leave the team short on shared reserves if there's a failure. This calculator matches turn points by volume.

Part of the Dive Tools toolkit by Chris Uriarte

Units:
Usable gas: %

Diver A

cu ft
psi
 
psi

Diver B

cu ft
psi
 
psi

Matched Turn Pressures

Pitfall: what happens if you use pressure-only thirds?
Safety reminder: Even with SAC-aware matching enabled, this calculator assumes both divers share a constant depth profile, constant SAC, and no failures. Real dives add variability — workload, temperature, stress, equipment differences, and overhead environments all change consumption. Always follow your training agency's gas-management guidelines and build in margin. Never dive to the exact numbers.

THESE TOOLS ARE FOR REFERENCE PURPOSES ONLY. USE AT YOUR OWN RISK.