Best Mix & MOD
Set the depth, choose your pO2 ceiling, and read off the richest safe nitrox — with its MOD at both ceilings, the equivalent air depth and a live safety envelope.
Documented figures — verify depths and conditions locally on the day.
Deeper than about 40 m the honest answer stops being nitrox. Plan it on the Trimix Best Mix tool instead.
The maths, explained
Dalton’s law does all the work. Absolute pressure in seawater is P = depth ÷ 10 + 1 bar, and the oxygen your body feels is its partial pressure, pO2 = FO2 × P. Turn that round and the richest safe mix for a target depth is FO2 = pO2 ceiling ÷ P. At 30 m, P is 4 bar, so 1.4 ÷ 4 = 0.35 — EAN35.
The same algebra gives any mix its maximum operating depth: MOD = (ceiling ÷ FO2 − 1) × 10. We plan bottom gas at a working ceiling of 1.4 bar and treat 1.6 as a decompression ceiling, never a bottom target.
EAD converts a nitrox dive into its air-equivalent nitrogen exposure: EAD = (FN2 ÷ 0.79) × (depth + 10) − 10. Less nitrogen in the mix, shallower the equivalent — that is the entire point of nitrox.
This Is Exactly What We Teach On Advanced Nitrox
Choosing the mix is the easy half. Advanced Nitrox teaches you to carry it, switch to it and track your oxygen exposure — enriched blends all the way to 100% oxygen.
Checked, not trusted: the formulas on this page are pinned by 130 automated reference checks that run on every change — cross-validated against Subsurface’s published planner tests, the independent DecoTengu implementation, printed MOD tables and the team’s own Splash apps.
For training and planning purposes only. Analyse every mix before you breathe it and always dive within your certification.