Gas blending that calculates, not guesses.
Gas Blender Toolkit computes nitrox and trimix blends using a real-gas model (Van der Waals) instead of a rough approximation — free, ad-free, and usable offline.
No sign-up. No ads. Installable as an app and works offline at the fill station.
Why divers pick this over other blending calculators
Built by a diver for divers — focused on physical accuracy, not gimmicks.
A real real-gas model
Calculations use the Van der Waals equation instead of the ideal gas law — noticeably more accurate at high pressures and high helium fractions. Ideal-gas mode remains available too.
Several blending methods
Partial-pressure blending with a freely chosen fill order, the continuous ("delta gas") method, and topping off from a storage bank — whichever way you fill.
Specialist calculators for every setup
Scuba gas MOD/END, CCR diluent MOD/END with a PPO2 setpoint, and a PSCR model for the loop's oxygen fraction over time — niche features few other tools offer.
Cost calculation built in
Enter your O2, He and topoff gas prices once — the toolkit works out the cost of every fill automatically.
Offline-capable web app
Install it to your home screen or desktop; it keeps working at the fill station without an internet connection. No accounts, no forced cloud sync.
Multilingual & flexible units
German, English, Russian and Ukrainian. Metric or imperial — plus configurable standard gases and cylinder volumes.
One tool for every breathing-gas situation
Blending that does the thinking
Enter your current fill and the desired mix — the toolkit calculates how much oxygen, helium and topoff gas to add, and in what order.
- Freely chosen fill order (He→O2→topoff and others)
- Automatic volume matching between cylinders
- Switch between ideal-gas and real-gas models
Rebreather diving, fully covered
The CCR diluent MOD/END view shows mix, gas density and narcotic depth across the full depth range — for your chosen PPO2 setpoint.
- Configurable narcotic potency factor for O2 and He
- Warns when gas density or END limits are exceeded
PSCR: oxygen fraction over time
For passive semi-closed rebreathers, the toolkit simulates how the loop's FiO2 settles over time and depth — including the dump ratio of injected gas.
Three steps to your fill table
Enter your current fill
O2 and helium fractions plus pressure of your cylinder — by typing values or dragging sliders.
Set your desired mix
Enter the target O2/He at the target pressure, or pick one of your saved standard gases.
Read off the fill table
The toolkit shows how much O2, helium and topoff gas to add, and in what order.
Important: always verify every calculated mix yourself with an analyzer before breathing it.
Free on the web. Native apps for on the go.
The web version is entirely free, works offline, and keeps getting improved. If you prefer a native app on your home screen, it's available for a small one-time price on Google Play and the Apple App Store — built with Cordova from the same codebase as the web app.
Open the free web appReady for your next fill?
No installation needed — jump straight in from your browser.
Open Gas Blender Toolkit