Understanding Standard Atmospheres to Technical Atmospheres Conversion
The standard atmosphere (atm) is defined as exactly 101,325 pascals. The technical atmosphere (at) is an older metric engineering unit equal to one kilogram-force per square centimeter, or 98,066.5 pascals, once widely used on European pressure gauges. Converting atm to at reconciles the physics reference pressure with legacy industrial equipment and documentation that report pressures in kgf/cm².
Conversion Formula
To convert standard atmospheres to technical atmospheres, multiply by this factor:
Step-by-Step Example
Convert 25 standard atmospheres to technical atmospheres.
How to Convert Standard Atmospheres to Technical Atmospheres
Relate the physics reference pressure to the legacy kgf/cm² unit.
- Take the atm value: For example, 25 atm.
- Multiply by 1.033227: This gives the technical-atmosphere equivalent.
- Compute: .
- State the result: 25 standard atmospheres equals about 25.8307 at.
standard atmospheres to technical atmospheres conversion table
| standard atmospheres (atm) | technical atmospheres (at) |
|---|---|
| 0 | 0 |
| 1 | 1.033227 |
| 2 | 2.066455 |
| 3 | 3.099682 |
| 4 | 4.13291 |
| 5 | 5.166137 |
| 6 | 6.199365 |
| 7 | 7.232592 |
| 8 | 8.26582 |
| 9 | 9.299047 |
| 10 | 10.33227 |
| 15 | 15.49841 |
| 20 | 20.66455 |
| 25 | 25.83069 |
| 30 | 30.99682 |
| 40 | 41.3291 |
| 50 | 51.66137 |
| 60 | 61.99365 |
| 70 | 72.32592 |
| 80 | 82.6582 |
| 90 | 92.99047 |
| 100 | 103.3227 |
| 150 | 154.9841 |
| 200 | 206.6455 |
| 250 | 258.3069 |
| 300 | 309.9682 |
| 400 | 413.291 |
| 500 | 516.6137 |
| 600 | 619.9365 |
| 700 | 723.2592 |
| 800 | 826.582 |
| 900 | 929.9047 |
| 1000 | 1033.227 |
| 2000 | 2066.455 |
| 3000 | 3099.682 |
| 4000 | 4132.91 |
| 5000 | 5166.137 |
| 10000 | 10332.27 |
| 25000 | 25830.69 |
| 50000 | 51661.37 |
| 100000 | 103322.7 |
| 250000 | 258306.9 |
| 500000 | 516613.7 |
| 1000000 | 1033227 |
What is the standard atmosphere?
The standard atmosphere (atm) is a unit of pressure defined as a fixed reference value close to the average atmospheric pressure at sea level. It is widely used in chemistry, physics, engineering, and diving to express pressures relative to typical sea-level conditions.
Definition
The standard atmosphere is defined exactly as 101,325 pascals:
This is equivalent to 1013.25 hectopascals (millibars), 760 millimeters of mercury (torr), and about 14.6959 pounds per square inch. The value was fixed by the 10th General Conference on Weights and Measures (CGPM) in 1954.
Origin and History
Early pressure measurement grew from Evangelista Torricelli's 1643 barometer experiments, which showed the atmosphere supports a mercury column about 760 mm high. The "atmosphere" became a convenient reference for a whole unit of ambient pressure. In 1954 the CGPM adopted the exact value 101,325 Pa, based on a 760 mm mercury column at 0 °C under standard gravity, to remove the temperature and location dependence of earlier definitions.
Law and Notable Facts
The standard atmosphere is accepted for use with the SI but is not an SI unit; the SI unit of pressure is the pascal. IUPAC now recommends the bar (100,000 Pa) rather than the atmosphere as the standard pressure for reporting thermodynamic data, though "atm" remains common. Note that the technical atmosphere (at) is a different unit equal to 98,066.5 Pa.
Real-World Examples and Conversions
- Average sea-level air pressure is very close to 1 atm (101.325 kPa).
- Ocean pressure increases by roughly 1 atm for every 10 meters of seawater depth, so a diver at 30 m experiences about 4 atm total.
- A typical car tire inflated to 32 psi holds about 2.2 atm of gauge pressure.
- The pressure inside a champagne bottle is roughly 6 atm (about 608 kPa).
What is the technical atmosphere?
The technical atmosphere (at) is a non-SI unit of pressure equal to one kilogram-force per square centimeter. It was widely used in engineering, especially in Europe, before the pascal became standard.
Definition
The technical atmosphere is defined as the pressure of one kilogram-force acting on one square centimeter:
This equals exactly 1 kgf/cm² (98,066.5 Pa), because standard gravity is 9.80665 m/s². It is close to, but distinct from, the standard atmosphere (atm = 101,325 Pa) and the bar (100,000 Pa).
Origin and History
The technical atmosphere arose from the gravitational metric system of units, which used the kilogram-force rather than the newton. Expressing pressure as kilogram-force per square centimeter was intuitive for engineers weighing loads, and the unit became common in mechanical and hydraulic engineering, boilers, and pneumatics through much of the 20th century.
Law and Notable Facts
The technical atmosphere is not part of the SI and its use is discouraged in favor of the pascal or bar. It is easily confused with the standard atmosphere; the two differ by about 3.3%. Gauge and absolute variants were often written "atü" (gauge) and "ata" (absolute) in German-language engineering.
Real-World Examples and Conversions
- 1 at = 1 kgf/cm² = 98.0665 kPa ≈ 0.9678 atm.
- 1 at ≈ 14.223 psi, close to but slightly below the 14.696 psi of one standard atmosphere.
- A pressure of 10 at (about 981 kPa) is a common rating benchmark for industrial hydraulic components.
- 1 at ≈ 0.980665 bar, so the bar and technical atmosphere differ by under 2%.
Frequently Asked Questions
How many technical atmospheres equal one standard atmosphere?
One standard atmosphere equals 1.033227 technical atmospheres.
How do I convert technical atmospheres back to atm?
Multiply the at value by 0.9678411. So 1 at equals about 0.968 atm.
What is the difference between atm and at?
The standard atmosphere is 101,325 Pa, while the technical atmosphere is 1 kgf/cm² = 98,066.5 Pa, so they differ by about 3.3%.
Where is the technical atmosphere still seen?
It appears on older European compressors, boilers, and gauges labeled in kgf/cm², where at rather than atm was the working unit.
What is 10 atm in technical atmospheres?
Multiply 10 by 1.033227 to get 10.33227 at.
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Complete standard atmospheres conversion table
| Unit | Result |
|---|---|
| pascals (Pa) | 101325 Pa |
| kilopascals (kPa) | 101.325 kPa |
| megapascals (MPa) | 0.101325 MPa |
| hectopascals (hPa) | 1013.25 hPa |
| millibar (mbar) | 1013.25 mbar |
| bar (bar) | 1.01325 bar |
| torr (torr) | 760 torr |
| meters of water @ 4°C (mH2O) | 10.33227 mH2O |
| millimeters of mercury (mmHg) | 759.9999 mmHg |
| centimeters of water (cmH2O) | 1033.227 cmH2O |
| technical atmospheres (at) | 1.033227 at |
| centimeters of mercury (cmHg) | 75.99999 cmHg |
| pounds per square inch (psi) | 14.69595 psi |
| kilopound per square inch (ksi) | 0.01469595 ksi |
| Inches of mercury (inHg) | 29.92126 inHg |