- Simple meaning
- Gas flow through a leak under a pressure difference
- Core formula
- Leak rate = pressure change x volume / time
- Main units
- Pa·m³/s, mbar·L/s, atm·cc/s, sccm
- Reading the number
- A smaller leak rate means a tighter part
Leak rate tells how much gas passes through a leak in a set time. Because gas is compressible, useful leak-rate units combine pressure, volume, and time.
For helium leak testing, Pa·m³/s and mbar·L/s are common in vacuum work. atm·cc/s and sccm are common in U.S. leak-test specifications and flow-style discussions.
Definition
What leak rate means
Leak rate = pressure change x volume / time. If a sealed 1 m³ evacuated vessel rises by 1 Pa in 1 second, the leak rate is 1 Pa·m³/s.
The same idea in mbar·L/s: if a 1 L vessel changes by 1 mbar in 1 second, the leak rate is 1 mbar·L/s.
Unit names
Common units
Pa·m³/s
SI-style leak-rate unit. Common in vacuum and helium leak detection specifications.
mbar·L/s
Very common helium leak testing unit. 1 Pa·m³/s = 10 mbar·L/s.
atm·cc/s
Atmosphere cubic centimeters per second. It is close to mbar·L/s, but not exactly the same.
sccm
Standard cubic centimeters per minute. 1 atm·cc/s = 60 sccm.
Quick reference
Useful conversions and common mistakes
- 1 Pa·m³/s = 10 mbar·L/s = about 9.87 atm·cc/s = about 592 sccm.
- 1 mbar·L/s = about 0.987 atm·cc/s = about 59.2 sccm.
- 1 atm·cc/s = 1.013 mbar·L/s = 0.101 Pa·m³/s = 60 sccm.
- 1 Torr·L/s = 1.333 mbar·L/s.
- ppm is concentration, not leak rate. It is useful for sniffer or accumulation tests, but it depends on sampling flow, volume, and timing.
- g/a (g/year) and %/year are application units. They must be tied to the product gas, internal volume, pressure, and acceptance rule.
Need to convert a leak rate?
Use the Wayeal converter for quick comparisons between Pa·m³/s, mbar·L/s, atm·cc/s, Torr·L/s, and sccm.
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