Hardly any measured value comes in as many units as the leak rate: mbar·l/s in Europe, atm·cc/s in America, Pa·m³/s per SI, sccm on flow devices. The Leak Rate Converter (Leak Testing) translates between all of them – and on request converts the helium reading into an air leak rate.
The units at a glance
All leak rate units describe the same thing: a pV throughput (pressure × volume per time). The key factors: 1 mbar·l/s = 0.1 Pa·m³/s ≈ 0.987 atm·cc/s ≈ 59.2 sccm. Once you understand the reference quantities, you see: the difference is pure scaling – things only get critical when the gas species changes.
Step by step
- Enter the measured leak rate: value and unit from the leak detector, e.g. 1×10⁻⁷ mbar·l/s
- Choose the target unit: all common units are displayed in parallel
- Activate gas conversion: helium → air, with selection of the flow regime
- Rank the result: the calculator places the leak rate into typical tightness classes
The trap: helium is not air
A leak measured with helium does not pass air to the same extent – and the conversion factor depends on the flow regime. In molecular flow (small leaks, high vacuum) the throughput scales with 1/√M: air flows slower than helium by a factor of √(4/29) ≈ 0.37. In laminar flow (larger leaks) viscosity governs – air sits only about 8% below helium. The same leak, two different factors: at 10⁻⁷ mbar·l/s of helium this corresponds to 3.7×10⁻⁸ or 9.3×10⁻⁸ mbar·l/s of air depending on the regime.
Practical ranking
Rules of thumb for specifications: 10⁻³ mbar·l/s can be heard hissing, 10⁻⁵ is watertight, from 10⁻⁷ a system counts as technically tight for high vacuum, semiconductor applications often demand 10⁻⁹ and better. For acceptance tests, the reference condition defined in the test protocol always governs – gas species, pressure difference and temperature belong to every serious leak rate statement.
