Understanding technical atmospheres to centimeters of water Conversion
A technical atmosphere is defined as one kilogram-force per square centimeter, equal to 98,066.5 pascals. A centimeter of water (cmH2O) is the pressure of a 1-centimeter water column, about 98.0665 pascals, used in respiratory medicine and low-pressure engineering. Conveniently, one technical atmosphere equals exactly 1,000 centimeters of water, since both derive from the same gravitational definition.
Conversion Formula
To convert technical atmospheres to centimeters of water, multiply by this factor:
Step-by-Step Example
Convert 25 technical atmospheres to centimeters of water.
How to Convert technical atmospheres to centimeters of water
Convert technical atmospheres to centimeters of water easily.
- Note the pressure: Start with the technical atmosphere value, e.g. 25.
- Multiply by 1000: Each technical atmosphere is 1,000 cmH2O.
- Give the result: 25 at \times 1000 = 25000 cmH2O.
technical atmospheres to centimeters of water conversion table
| technical atmospheres (at) | centimeters of water (cmH2O) |
|---|---|
| 0 | 0 |
| 1 | 1000 |
| 2 | 2000 |
| 3 | 3000 |
| 4 | 4000 |
| 5 | 5000 |
| 6 | 6000 |
| 7 | 7000 |
| 8 | 8000 |
| 9 | 9000 |
| 10 | 10000 |
| 15 | 15000 |
| 20 | 20000 |
| 25 | 25000 |
| 30 | 30000 |
| 40 | 40000 |
| 50 | 50000 |
| 60 | 60000 |
| 70 | 70000 |
| 80 | 80000 |
| 90 | 90000 |
| 100 | 100000 |
| 150 | 150000 |
| 200 | 200000 |
| 250 | 250000 |
| 300 | 300000 |
| 400 | 400000 |
| 500 | 500000 |
| 600 | 600000 |
| 700 | 700000 |
| 800 | 800000 |
| 900 | 900000 |
| 1000 | 1000000 |
| 2000 | 2000000 |
| 3000 | 3000000 |
| 4000 | 4000000 |
| 5000 | 5000000 |
| 10000 | 10000000 |
| 25000 | 25000000 |
| 50000 | 50000000 |
| 100000 | 100000000 |
| 250000 | 250000000 |
| 500000 | 500000000 |
| 1000000 | 1000000000 |
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%.
What is the centimeter of water?
The centimeter of water (cmH2O) is a unit of pressure equal to the pressure exerted by a one-centimeter-high column of water under standard conditions. It is used heavily in medicine and respiratory therapy, where small pressures are common.
Definition
The conventional centimeter of water is defined as the pressure of a 1 cm column of water with a density of 1000 kg/m³ under standard gravity (9.80665 m/s²):
This is the conventional value. Because water density varies with temperature, more precise variants exist (for example, cmH2O at 4 °C uses water's maximum density of about 999.972 kg/m³, giving roughly 98.064 Pa).
Origin and History
The unit comes directly from the water manometer, an instrument in which pressure is read as the height difference of a water column. Water was chosen for low pressures because it produces a taller, more readable column than mercury (water is about 13.6 times less dense). The convention fixes water density and gravity so the unit has a single agreed value independent of local conditions.
Law and Notable Facts
The centimeter of water is not an SI unit but is permitted in medical contexts, where it remains standard for measuring airway, ventilator, and cerebrospinal-fluid pressures. Roughly 1 cmH2O equals 0.7356 mmHg, so about 1.36 cmH2O make up 1 mmHg.
Real-World Examples and Conversions
- Mechanical ventilators typically deliver positive end-expiratory pressure (PEEP) of 5 to 10 cmH2O.
- Normal cerebrospinal-fluid opening pressure in a lumbar puncture is roughly 10 to 18 cmH2O.
- 1 cmH2O ≈ 98.0665 Pa ≈ 0.098 kPa.
- A standard atmosphere equals about 1033.2 cmH2O.
Frequently Asked Questions
How many centimeters of water are in one technical atmosphere?
One technical atmosphere equals exactly 1,000 centimeters of water.
How many technical atmospheres are in a cmH2O?
One centimeter of water equals 0.001 technical atmospheres.
What is a centimeter of water used for?
It measures low pressures in ventilators, CPAP machines, and manometers, equal to about 98.07 pascals.
Why is the factor exactly 1000?
Both units are built on the kilogram-force and standard gravity, so the ratio between them is an exact power of ten.
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Complete technical atmospheres conversion table
| Unit | Result |
|---|---|
| pascals (Pa) | 98066.5 Pa |
| kilopascals (kPa) | 98.0665 kPa |
| megapascals (MPa) | 0.0980665 MPa |
| hectopascals (hPa) | 980.665 hPa |
| millibar (mbar) | 980.665 mbar |
| bar (bar) | 0.980665 bar |
| torr (torr) | 735.5592 torr |
| meters of water @ 4°C (mH2O) | 10 mH2O |
| millimeters of mercury (mmHg) | 735.5591 mmHg |
| standard atmospheres (atm) | 0.9678411 atm |
| centimeters of water (cmH2O) | 1000 cmH2O |
| centimeters of mercury (cmHg) | 73.55591 cmHg |
| pounds per square inch (psi) | 14.22334 psi |
| kilopound per square inch (ksi) | 0.01422334 ksi |
| Inches of mercury (inHg) | 28.95902 inHg |