Blending calculator
Calculate how many bars of oxygen, helium and top-off gas to add to the gas already in the tank to get the desired mix, using the partial pressure method.
Residual gas in tank
Desired mix
How to fill
- 1.Add Oxygen:+27.8 bar(from 50 to 77.8 bar)
- 2.Add Air (21%):+122.2 bar(from 77.8 to 200 bar)
Pure oxygen
27.8 bar
417.7 L
Helium
0 bar
0 L
Top-off gas
122.2 bar
1832.3 L
Target mix MOD: 33.8 m at PpO₂ 1.4 · 40 m at PpO₂ 1.6. Values are calculated with the ideal gas model and do not account for compressibility or heating during the fill: always verify the mix with an analyzer.
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Frequently asked questions
How does partial pressure blending work?
You add each gas until its partial pressure matches the target mix: helium first, then oxygen, then top up with air or nitrox. The calculator converts the target fractions into bar to add.
Can I blend nitrox from a partly full cylinder?
Yes. Enter the residual pressure and its oxygen and helium content and the calculator accounts for the gas already in the cylinder.
Is gas blending safe to do at home?
Handling oxygen requires oxygen-clean equipment, oxygen-compatible lubricants and formal blender training. Always follow your agency and filling station procedures.
How do I check a blended mix?
Always analyse the cylinder with an oxygen (and helium, for trimix) analyser after filling, label it, and confirm the MOD before diving.