Torr to Pound per Square Inch
Torr
psi
Conversion History
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Quick Reference Table (Torr to Pound per Square Inch)
| Torr (Torr) | Pound per Square Inch (psi) |
|---|---|
| 0.001 | 0.00001933677470480251670458028512408916 |
| 0.01 | 0.00019336774704802516704435247386357604 |
| 0.1 | 0.00193367747048025167044207436125844484 |
| 1 | 0.01933677470480251670442219398996176396 |
| 10 | 0.19336774704802516704421613839010837736 |
| 760 | 14.69594877564991269536047728085644272396 |
| 7,600 | 146.95948775649912695360477861007393650184 |
About Torr (Torr)
The torr is a unit of pressure equal to exactly 1/760 of a standard atmosphere, approximately 133.322 pascals — differing from the mmHg by less than 0.00015%. The torr is the dominant unit in vacuum science, surface chemistry, thin-film deposition, and mass spectrometry. High vacuum systems operate at 10⁻³–10⁻⁶ torr; ultra-high vacuum (UHV) below 10⁻⁹ torr. The torr provides convenient order-of-magnitude values across the full vacuum range from atmospheric pressure to the limits of laboratory pumping.
Freeze-drying food operates at 0.1–4 torr. The interior of a sealed vacuum tube operates at roughly 10⁻⁶ torr.
Etymology: Named after Evangelista Torricelli (1608–1647), Italian physicist and mathematician who invented the mercury barometer in 1643 and first accurately measured atmospheric pressure as the height of a mercury column.
About Pound per Square Inch (psi)
The pound per square inch (psi) is the dominant pressure unit in US customary practice, equal to approximately 6,894.76 pascals. It is universally used in the United States for tire pressures, compressed-air systems, hydraulic machinery, pipe pressure ratings, and industrial gauges. Standard atmospheric pressure is 14.696 psi. Pressure is expressed as gauge (psig, relative to atmosphere) or absolute (psia). Natural gas pipeline pressures, boiler ratings, and municipal water supply pressures in the US are all quoted in psi.
Car tire inflation is typically 30–35 psi. A standard garden hose delivers water at 40–60 psi.
Etymology: A straightforward compound of "pound" (from Latin pondus, weight) and "square inch", arising naturally from US customary engineering practice. There is no single defining event; the unit crystallised alongside the development of American steam engineering in the early 19th century.
Torr – Frequently Asked Questions
Can you actually create a perfect vacuum of 0 torr?
No — a true 0 torr vacuum is physically impossible. Even the best laboratory cryo-pumps bottom out around 10⁻¹³ torr, where stray molecules still occasionally wander through. Interstellar space is roughly 10⁻¹⁷ torr but still contains a few hydrogen atoms per cubic centimeter. Quantum field theory predicts that even "empty" space seethes with virtual particle pairs, so absolute nothingness does not exist. In practice, engineers define "good enough" vacuum levels for each application — 10⁻³ torr for freeze-drying, 10⁻⁶ for electron microscopes, 10⁻⁹ for particle accelerators.
Why is the torr the go-to unit in vacuum science?
Because the torr maps neatly to the range of vacuum pressures: rough vacuum is 1–760 torr, medium vacuum 10⁻³–1 torr, high vacuum 10⁻⁶–10⁻³ torr, and ultra-high vacuum below 10⁻⁹ torr. Each regime is a clean power of ten. Expressing the same range in pascals (133,000 down to 0.00000013 Pa) is clumsy. The torr gives vacuum engineers a log-friendly scale that spans thirteen orders of magnitude in tidy notation.
How low a vacuum can modern labs achieve in torr?
Routine lab turbo-pump systems reach 10⁻⁸ torr. Particle accelerators like CERN's LHC operate at about 10⁻¹⁰ torr — comparable to the vacuum of outer space near the Moon. The lowest laboratory pressure ever achieved is around 10⁻¹³ torr, using cryogenic pumps at liquid-helium temperatures. At that level, a molecule might travel thousands of kilometers before hitting another molecule.
What everyday processes rely on partial vacuum measured in torr?
Freeze-drying food and pharmaceuticals operates at 0.1–4 torr. Vacuum-sealed food storage bags pull to about 5–10 torr. Incandescent light bulbs were historically evacuated to ~0.01 torr. Vacuum-assisted braking in cars uses roughly 400–500 torr of manifold vacuum. Even your thermos flask has a vacuum of perhaps 10⁻³ torr between its double walls to block heat conduction.
What happens to boiling points as torr drops inside a vacuum chamber?
Boiling point plummets. Water boils at 100 °C at 760 torr (sea level), but at only 25 °C at about 24 torr and at 0 °C at just 4.6 torr. This is how freeze-drying works: reduce pressure to 0.1–1 torr and ice sublimates directly to vapor without ever becoming liquid. Vacuum distillation in chemistry exploits the same principle — heat-sensitive compounds that would decompose at their normal boiling point can be distilled gently at a fraction of the temperature under reduced torr.
Pound per Square Inch – Frequently Asked Questions
Why do race car teams obsess over half-psi differences in tire pressure?
Because at racing speeds, tiny pressure changes transform tire behavior. Half a psi less inflates the contact patch, generating more grip but also more heat — potentially pushing the rubber past its optimal temperature window within a few laps. Half a psi more stiffens the sidewall, improving response but shrinking the contact patch and reducing peak grip. Formula 1 teams adjust pressures in quarter-psi increments based on track temperature, fuel load, and stint length. In NASCAR, a 1 psi difference between left and right tires is a deliberate setup tool that changes how the car rotates through banked turns.
What psi should car and bicycle tires be inflated to?
Passenger car tires: 30–35 psi (check the door jamb sticker, not the tire sidewall — the sidewall shows the maximum, not the recommended). Truck tires: 80–100 psi. Road bike tires: 80–130 psi. Mountain bike tires: 25–35 psi. Under-inflation by just 5 psi increases fuel consumption by about 2% and accelerates edge wear. Over-inflation reduces grip and makes the ride harsh.
What is the difference between psi, psig, and psia?
PSI is the generic unit. PSIG ("gauge") means pressure above atmospheric — what your tire gauge reads. PSIA ("absolute") includes atmospheric pressure on top: PSIA = PSIG + 14.7. A tire at 32 psig is actually at 46.7 psia. The distinction matters in engineering calculations involving gas laws (PV=nRT uses absolute pressure) and in vacuum work where gauge readings go negative.
What psi range do common household and industrial systems use?
City water supply: 40–80 psi. Home espresso machine: ~130 psi (9 bar). Pressure washer: 1,000–4,000 psi. Scuba tank: 3,000 psi. Hydraulic car jack: 3,000–10,000 psi. Diesel fuel injector rail: up to 30,000 psi. Waterjet cutter: 60,000+ psi. The range from a garden hose to an industrial waterjet spans roughly three orders of magnitude.
How do you quickly convert between psi and bar in your head?
Divide psi by 14.5 to get bar, or multiply bar by 14.5 to get psi. For even quicker estimates: 15 psi ≈ 1 bar, 30 psi ≈ 2 bar, 45 psi ≈ 3 bar. This "15 psi per bar" shortcut is within 2% of exact and is used by mechanics, divers, and engineers worldwide when a calculator is not handy.