Vacuum converter
Convert vacuum pressure between millibar, torr and microns, and see how much gas is actually left.
That's about the same as high vacuum. That is about 9.869×10⁻⁸% of atmospheric pressure still in there.
What it means
How empty is it?
Molecule counts and mean free paths are for air at 20 °C. A gauge reading also depends on which gas it was calibrated for.
Every unit
Your vacuum in every unit
Learn
Three things worth knowing
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1 micron = 1 millitorr
Vacuum pumps are rated in microns of mercury, which is the same as a millitorr, or 0.00133 mbar.
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Mean free path decides everything
At atmospheric pressure a molecule flies 65 nm before colliding; at 10⁻⁶ mbar it flies 65 meters. That is why coating and electron beams need high vacuum.
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Gauge vacuum is not absolute
A shop gauge reading "29 inHg of vacuum" means about 33 mbar absolute, not zero. Vacuum science always works in absolute pressure.
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Popular vacuum conversions
Background
About vacuum ranges
Vacuum work spans fifteen orders of magnitude, and each decade behaves differently. At 1 mbar air still flows like a fluid. At 10⁻⁶ mbar molecules fly in straight lines between walls. At 10⁻⁹ a clean surface stays clean for hours.
Even at 10⁻⁹ mbar there are still 25 million molecules in every cubic centimeter.