Nitrox & Trimix Gas Blender

You add oxygen until its partial pressure matches your target, then top with air. This tool gives the oxygen fill pressure for a target mix, accounting for what is already in the tank, in ideal-gas or real-gas mode.

You add helium first, then oxygen, then top off with air or a banked mix, each to a calculated pressure. Switch this tool to Trimix and it gives all three fill pressures for a target mix, accounting for what is already in the tank.

Helium banks usually sit at lower pressure than oxygen banks, so decanting helium into a near-empty tank wastes the least gas, and adding the denser oxygen and top-off gas afterwards helps the light helium mix through the cylinder. Whatever order you fill in, always analyse the mix before diving it.

Ideal-gas maths assume perfectly linear compression; real-gas (van der Waals) corrections account for the fact that gases do not, which matters at higher fill pressures. Helium deviates in the opposite direction to oxygen and nitrogen, so ideal maths leave a trimix slightly lean on helium. Real-gas mode gives a more accurate fill.

A mix with less than about 18% oxygen, which cannot reliably support consciousness at the surface. Deep blends like 10/70 are hypoxic: you need a travel gas for the shallow part of the dive, and this tool flags any hypoxic result.

Yes. Enter the starting pressure and mix plus the gas you are adding, and the tool returns the final blend so you can check a top-off before diving it. Always analyse the cylinder before use.