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The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2] The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is ...
Bar Technical atmosphere Standard atmosphere Torr Pound per square inch (Pa) (bar) (at) (atm) (Torr) (lbf/in 2) 1 Pa — 1 Pa = 10 −5 bar 1 Pa = 1.0197 × 10 −5 at 1 Pa = 9.8692 × 10 −6 atm 1 Pa = 7.5006 × 10 −3 Torr 1 Pa = 0.000 145 037 737 730 lbf/in 2: 1 bar 10 5 — = 1.0197 = 0.986 92 = 750.06 = 14.503 773 773 022: 1 at 98 066.5 ...
133 Pa 1 torr ≈ 1 mmHg [34] ±200 Pa ~140 dB: Threshold of pain pressure level for sound where prolonged exposure may lead to hearing loss [citation needed] ±300 Pa ±0.043 psi Lung air pressure difference moving the normal breaths of a person (only 0.3% of standard atmospheric pressure) [35] [36] 400–900 Pa 0.06–0.13 psi
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
It is also equivalent to 10 barye (10 Ba) in the CGS system. Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to one millibar, and the kilopascal (1 kPa = 1000 Pa), which is equal to one centibar. The unit of measurement called standard atmosphere (atm) is defined as 101,325 Pa. [2]
The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N/m 2, or kg·m −1 ·s −2). This name for the unit was added in 1971; [7] before that, pressure in SI was expressed in newtons per square metre. Other units of pressure, such as pounds per square inch (lbf/in 2) and bar, are also in common use.
In SI units, the unit is converted to the SI derived unit pascal (Pa), which is defined as one newton per square metre (N/m 2). A newton is equal to 1 kg⋅m/s 2, and a kilogram-force is 9.80665 N, [3] meaning that 1 kgf/cm 2 equals 98.0665 kilopascals (kPa).
The bar is defined using the SI derived unit, pascal: 1 bar ≡ 100,000 Pa ≡ 100,000 N/m 2. Thus, 1 bar is equal to: 1,000,000 Ba (in cgs units); and 1 bar is approximately equal to: 0.98692327 atm; 14.503774 psi; 29.529983 inHg; 750.06158 mmHg; 750.06168 Torr; 1019.716 centimetres of water (cmH 2 O) (1 bar approximately corresponds to the ...