Enter a PSI reading to find its equivalent absolute pressure in Torr, with an option for gauge readings marked psig.
Advanced options
The 14.6959 psi value is a NIST standard-atmosphere planning estimate for the United States. Replace it with a local barometer, procedure, or equipment value when needed.
Table of contents
How to use our PSI to Torr Converter
- Enter the pressure number from your gauge, equipment label, datasheet, worksheet, or calculation.
- For a reading marked psia or absolute, leave the Advanced option set to "PSI treated as absolute."
- For a reading marked psig or gauge, choose "PSI gauge pressure" and check the atmospheric-pressure value. Replace it with a local absolute-pressure reference if your procedure provides one.
- Click Calculate. Use the first result as the absolute pressure in Torr, then check the interpretation note to make sure it matches the label on your source.
Definitions
PSI: Pounds per square inch, a pressure unit commonly used in the United States.
Torr: An absolute-pressure unit. Zero Torr is zero absolute pressure, also called a perfect vacuum.
Absolute pressure: Pressure measured from a perfect vacuum. A reading marked psia is absolute pressure.
Gauge pressure: Pressure measured relative to the surrounding air pressure. A reading marked psig needs an atmospheric-pressure reference before it can be converted to absolute Torr.
Atmospheric pressure: The pressure of the surrounding air. The calculator's gauge setting starts with 14.6959 psi absolute, a rounded standard-atmosphere value. [1]
Common mistakes and quick fixes
Mistake: Treating a reading marked psig as though it were psia.
Fix: Choose "PSI gauge pressure" so the atmospheric-pressure reference is added before conversion.
Mistake: Assuming an unlabeled PSI value is absolute pressure.
Fix: Check the gauge face, datasheet, or procedure for psia, psig, absolute, or gauge. The number alone does not identify its reference.
Mistake: Using standard atmosphere when the procedure requires local conditions.
Fix: Replace the default atmospheric value with the stated or measured local absolute atmospheric pressure.
Mistake: Entering a negative gauge reading that is lower than the atmospheric reference.
Fix: Check both entries. Gauge pressure plus atmospheric pressure must be at least 0 psi absolute.
Mistake: Writing a decimal with a comma, such as 1,01 psi.
Fix: Use a decimal point for decimals, such as 1.01. Use commas only in whole-number thousands, such as 1,000.
Mistake: Rounding PSI before converting it.
Fix: Enter the digits available from the source, then select the needed number of result decimal places.
Limitations & Key Assumptions / Boundary Conditions
- The conversion changes pressure units only. It does not correct a faulty gauge, sensor calibration, temperature effect, or measurement setup.
- In gauge mode, the answer depends on the atmospheric-pressure reference. Local atmospheric pressure can differ from the default standard-atmosphere value.
- A negative gauge reading is possible, but gauge pressure plus the atmospheric reference cannot be below 0 psi absolute.
- Displayed decimal places round the result. Keep enough digits for a technical specification or later calculation.
- The calculator cannot determine whether an unlabeled PSI reading is absolute or gauge pressure.
Methodology
Conversion method
The calculator first finds absolute pressure in psi. An absolute input is used unchanged. For a gauge input, it adds the selected atmospheric-pressure reference because Torr is an absolute-pressure unit.
absolute pressure (psi) = entered pressure (psi)
absolute pressure (psi) = gauge pressure (psi) + atmospheric pressure (psi absolute)
It then multiplies absolute pressure by 51.7149325716 Torr per psi, using the NIST pressure conversion relationship. [1]
pressure (Torr) = absolute pressure (psi) x 51.7149325716
Worked example
An absolute reading of 2.5 psi gives 2.5 x 51.7149325716 = 129.287331429 Torr. At four decimal places, the displayed value is 129.2873 Torr. A reading of 0 psig with the default 14.6959 psi atmospheric reference becomes 14.6959 psi absolute, or about 759.9975 Torr.
Calculation choices
Result decimal places change only the displayed rounding, not the calculation. The default atmospheric reference is a standard-atmosphere planning value and can be replaced for gauge-pressure work that specifies local conditions.