← Back to Articles

Vacuum unit conversion basics

Understanding Torr, mbar, Pa, and other vacuum pressure units used in CVD and etch processes.

By Semiconductor Tools Editorial Team · Last updated: 2026-06-14

Semiconductor vacuum equipment uses a patchwork of pressure units depending on vendor origin (US, EU, Japan), gauge type, and legacy recipe conventions. A process engineer must move fluently between Torr, mbar, Pa, microns (mTorr), and occasionally psi or bar when reading datasheets, chamber controllers, and leak-check procedures.

Reference conversion table

Atmospheric pressure and common vacuum-unit relationships:

  • 1 atm = 760 Torr = 1013.25 mbar = 101,325 Pa = 14.696 psi
  • 1 Torr ≈ 1.333 mbar ≈ 133.3 Pa
  • 1 mbar ≈ 0.750 Torr
  • 1 micron (µm Hg) = 1 mTorr = 10⁻³ Torr

Worked example — Recipe pressure in multiple units with Pressure Unit Converter

A PECVD recipe specifies chamber pressure 2.5 Torr. A European gauge reads mbar; a SI-based RGA report uses Pa.

  1. Open Pressure Unit Converter, enter 2.5, From Unit: Torr.
  2. Read all outputs: ≈ 3.333 mbar, ≈ 333.3 Pa, ≈ 0.00333 bar, ≈ 0.0483 psi.
  3. Verify alarm setpoints on the tool PLC are consistent—e.g., high-pressure abort at 3.0 Torr = 4.0 mbar, not 3.0 mbar (a common entry error).

Worked example — Base pressure specification

Chamber qualification requires base pressure < 5×10⁻⁷ Torr.

  1. Enter 5e-7 Torr in the Pressure Converter.
  2. Equivalent: 6.67×10⁻⁷ mbar, 6.67×10⁻⁵ Pa.
  3. When comparing against a gauge reading in mbar, ensure exponent signs are not confused during manual conversion.

Practical guidance

Always record the unit alongside the number in recipes, SPC charts, and handoff logs. When combining pressure with volume for rate-of-rise tests (qL = V·Δp/Δt), keep Δp in the same unit system as your throughput target—our Throughput & Leak Rate Converter handles Torr, mbar, and Pa consistently.