sccm → Pumping Speed Calculator

Throughput and Pumping Speed

In vacuum systems, throughput (Q) is the gas load pumped per unit time, expressed as pressure × volumetric flow (e.g. Torr·L/s). Pumping speed (S) is the volume of gas removed per unit time (L/s). At steady state, the fundamental relationship is:

Q = S × P

Therefore, the required pumping speed is S = Q / P. Given gas flow (e.g. sccm from MFC) and chamber pressure, you can calculate the minimum pump speed needed to maintain that pressure.

Conversion: sccm → Q (Torr·L/s)

At STP (760 Torr, 0°C): 1 sccm = 760 × (10⁻³/60) ≈ 0.01267 Torr·L/s. For 1 slm: Q ≈ 12.67 Torr·L/s. The tool uses these conversion factors to compute Q from sccm or slm input.

Practical Applications

• Cryo capacity — Compare required S with cryo pump capacity to judge if cryo capacity is sufficient for the gas load.
• Throttle opening — With conductance-limited flow, effective S depends on throttle. Use S = Q/P to infer effective pump speed or throttle conductance.
• Chamber pressure not dropping — If pressure stays high despite pumping, compare actual Q (from MFC, leaks, outgassing) with pump capacity. If Q > S × P at target pressure, the pump cannot reach that pressure.