Best mix answers what should I breathe at this depth? Give it a depth, an oxygen limit and two targets, and it returns the mix that sits on those limits there. It is Mix at depth run backwards.

What you enter

• Depth (m): the deepest point the mix has to work at.
• Max ppO₂: 1.2, 1.4 or 1.6 bar at that depth.
• Max EAD (m): the narcosis target. The tool adds helium until the EAD is at or below it.
• Max density (g/L): the density target, handled the same way.

The Targets group notes that 30 m EAD and 5.2 g/L are common technical limits. Unlike the calculator in the planner’s gas wizard, both targets here are yours to change.

Reading the result

• Breathe: the mix, named as divers name it: Air, EAN32, Trimix 18/45.
• Oxygen and Helium (%): the two fractions, as whole percentages.
• EAD (m) and Density (g/L): what the mix gives at the depth, with your target beside each.
• The composition bar: the O₂, He and N₂ split, with each share in figures.

The mix is decided in two moves. Oxygen comes first: the richest whole percentage your Max ppO₂ allows at the depth, rounded down so the ppO₂ lands at or below your limit. Helium is then the least that meets both targets, rounded up, and whichever target needs more sets it. The verdict says which one did: past roughly 50 to 60 m it is usually density.

What it does not check

• The surface. A mix for 60 m at 1.3 bar comes to 18 % oxygen, too lean to breathe at the surface, and nothing says so. A hypoxic mix needs a travel gas.
• Decompression. The result is a bottom mix for one depth. Deco gases and their switch depths are separate decisions.
• What can be filled. The answer is what the limits ask for, not a mix rounded to what your blender stocks. Put the analysed mix, not this one, into a plan.

Next

• Mix at depth checks a mix you already have.
• Partial-pressure fill turns the result into a fill.
• Best mix in the planner covers the gas wizard’s version.