Torr to PSI Converter
Common Conversions
| torr | psi |
|---|---|
| 0.01 | 0.000193 |
| 0.1 | 0.001934 |
| 0.25 | 0.004834 |
| 0.5 | 0.009669 |
| 1 | 0.019337 |
| 2 | 0.038674 |
| 5 | 0.096686 |
| 10 | 0.193372 |
| 25 | 0.483429 |
| 50 | 0.966859 |
| 100 | 1.933718 |
| 1000 | 19.337 |
Why this conversion matters in chemistry
Freeze-dryer isolation valve sizing hits this regularly. A 1 torr chamber pressure vents to 14.68 psi atmospheric across the isolation valve — a 14,000-fold pressure ratio across the seat, which drives the shaft-seal torque specification on the valve body. A factor of 0.019337 psi per torr is just 1 atm = 760 torr = 14.696 psi. Mostly bookkeeping at the boundary of torr-graduated lab vacuum equipment and psi-stated industrial pneumatic hardware.
Formula
Where the factor comes from
This pair crosses a boundary the other pressure conversions do not — a subdivision of the atmosphere meeting a force divided by an area. The torr side is exactly 101325/760 Pa. The psi side descends from the international agreement fixing the avoirdupois pound at exactly 0.45359237 kg and the inch at exactly 25.4 mm, which together with standard gravity of exactly 9.80665 m/s² makes one psi exactly 8896443230521/1290320000 Pa, or 6894.757293168… The quotient is 0.019336774704…, exact in principle and non-terminating in practice. Read the other direction it says more: one psi is 51.71 torr. That reciprocal is what makes the pairing awkward — a unit sized for cylinder pressures being asked to describe a manifold.
Precision and significant figures
The factor is exact, so any figure lost in this conversion is lost to the display rather than the arithmetic. Going from torr to psi drives the magnitude down by a factor of fifty, and psi readouts and dials typically carry two decimal places at best. That resolution is 0.01 psi, or about half a torr — ample at cylinder pressures and hopeless in the single-digit torr range, where 1.0 and 1.2 torr both show as 0.02 psi. Six figures on 0.019337 are therefore beside the point; the constraint is that psi is the coarser scale here. When the vacuum range is what needs resolving, quote torr, or drop to pascals and let the exponent carry it.
Worked Examples
Standard atmospheric pressure — the anchor.
About a typical rotary-evaporator vacuum setting.
About a deep vacuum reading.
Half-atmosphere — about a reduced-pressure distillation setpoint.
Common mistakes
Under vacuum the psi figure goes negative
Torr is always absolute; psi on a shop gauge is almost always referenced to ambient. A chamber at 1 torr absolute is about −14.68 psig, not 0.019 psig, and the small positive number this conversion produces is correct only on a psia scale. Handing an absolute figure to a gauge-referenced instrument or specification quietly changes what is being described.
Specifying a vacuum setpoint in psi
Because one psi spans about 52 torr, a vacuum requirement written in psi carries almost no information. Asking for 0.02 psi when the process needs 1 torr leaves a tolerance band wider than the process window, and any rounding done at the psi stage arrives as several torr at the chamber. Write the requirement in torr or pascals and let the psi figure be the derived one.
A misplaced decade in 0.019337
Small factors with leading zeros invite decade slips, and this one conceals them well. Convert 100 torr with 0.19337 instead of 0.019337 and you get 19.3 psi — a number entirely at home on a regulator dial, sitting above atmospheric rather than well below it. The sanity check costs nothing: any pressure under one atmosphere has to land below 14.7 psia.