Throughput & Leak Rate Tools

Convert between common gas-flow and leak-rate units and analyze leak rate from pressure rise tests. Based on NIST conversion factors and standard vacuum engineering formulas.

Calculator

Converts between sccm, slm, mbar·L/s, Torr·L/s, and Pa·m³/s. Uses NIST factors (1 sccm = 0.0168875 mbar·L/s = 0.001689 Pa·m³/s).

Converted

0.016890 mbar·L/s

Canonical (Pa·m³/s)

0.001689 Pa·m³/s

Internal unit is SI throughput (Pa·m³/s). Use this value directly in energy/mass-balance style calculations.

Technical Explanation

Throughput and Leak Rate

In vacuum technology, throughput Q is defined as pressure × volumetric flow rate. Its natural SI unit is Pa·m³/s, which is dimensionally equivalent to power per unit area. Vacuum engineering also uses mbar·L/s or Torr·L/s as leak rate units.

Many process tools specify flows in sccm (standard cubic centimeters per minute). Using NIST conversion coefficients at standard conditions, this tool adopts:

1 sccm = 0.0168875 mbar·L/s = 0.001689 Pa·m³/s

Rate-of-Rise Method

In a pressure rise (rate-of-rise) test, the chamber is isolated from the pump and the pressure increase is measured from p₁ to p₂ over a time interval Δt. With volume V, the total gas load or leak rate is:

q_L = V · (Δp / Δt)

When expressed in mbar and liters, q_L has units of mbar·L/s. This method is widely used to quantify leaks and outgassing in vacuum systems with only a gauge and known volume.

Ultimate Pressure Estimate

With effective pumping speed S_eff and leak/gas load q_L, the approximate ultimate pressure is:

p_ult ≈ q_L / S_eff

If the measured base pressure is significantly higher than this estimate, either the effective pumping speed is lower than assumed or additional gas loads (outgassing, virtual leaks) are present.

References & Disclaimer

Conversion factors follow NIST gas flow unit conversion tables. Pressure-rise and leak-rate relationships follow standard vacuum engineering references (e.g., Leybold, Lesker). For critical applications, verify assumptions about standard conditions, gas species, and measurement accuracy.

Engineering Guide

Why this calculation matters

Leak specs, MFC loads, and pump budgets use different throughput units (sccm, mbar·L/s, Torr·L/s, Pa·m³/s). Rate-of-rise tests produce q_L that must compare directly with process gas load.

In semiconductor equipment work: Leak check documentation, converting MFC flow to vacuum load, rate-of-rise leak quantification, and ultimate pressure estimates p ≈ q/S.

Input parameters

Throughput value
Flow or leak rate in sccm, slm, mbar·L/s, Torr·L/s, or Pa·m³/s.
Rate-of-rise fields
Volume V, p₁, p₂, Δt for q_L = V·Δp/Δt.
Optional S_eff
For ultimate pressure estimate p_ult ≈ q/S.

Output interpretation

Unit conversions
Equivalent throughput in all supported units.
Leak rate q_L
From isolated chamber pressure rise.

If q_L from rate-of-rise exceeds spec only after PM, suspect seal or feedthrough. Compare process MFC Q (converted from sccm) only when MFCs are closed for leak tests.

Assumptions

  • STP sccm conversion: 1 sccm ≈ 0.0168875 mbar·L/s.
  • Uniform chamber volume; isolated from pump during rate-of-rise.
  • Ideal gas for Δp/Δt linearization over the measurement window.

Limitations

  • Temperature drift during rate-of-rise adds uncertainty.
  • Outgassing during isolation is included in q_L — not pure leak.
  • Large Δp may need log-mean pressure correction for high accuracy.

Worked example

Rate-of-rise after PM — V = 150 L

  1. p rises 2e-6 → 8e-6 Torr in 600 s.
  2. q_L ≈ 1.5e-6 Torr·L/s.
  3. With S_eff = 80 L/s → p_ult ≈ 1.9e-8 Torr predicted floor from this load alone.