Understanding Centimeters of Mercury to Technical Atmospheres Conversion
A centimeter of mercury (cmHg) is a mercury-column pressure unit, while a technical atmosphere (at) is defined as one kilogram-force per square centimeter, roughly 98066.5 pascals. The technical atmosphere is common in older European and engineering literature for boilers, hydraulics, and pressure vessels. Converting cmHg to technical atmospheres lets mercury-based readings align with that kgf/cm² framework.
Conversion Formula
To convert centimeters of mercury to technical atmospheres, multiply by this factor:
Step-by-Step Example
Convert 25 centimeters of mercury to technical atmospheres.
How to Convert Centimeters of Mercury to Technical Atmospheres
Rescale a mercury-column pressure into the kilogram-force-per-square-centimeter technical atmosphere.
- Note the cmHg value: Start with the pressure in centimeters of mercury.
- Multiply by 0.0135951: This factor gives the pressure in technical atmospheres.
- Report the result: For example, 25 cmHg × 0.0135951 = 0.339878 at.
- Reverse if needed: Multiply the technical-atmosphere value by 73.55591 to recover cmHg.
centimeters of mercury to technical atmospheres conversion table
| centimeters of mercury (cmHg) | technical atmospheres (at) |
|---|---|
| 0 | 0 |
| 1 | 0.0135951 |
| 2 | 0.0271902 |
| 3 | 0.0407853 |
| 4 | 0.0543804 |
| 5 | 0.0679755 |
| 6 | 0.0815706 |
| 7 | 0.0951657 |
| 8 | 0.1087608 |
| 9 | 0.1223559 |
| 10 | 0.135951 |
| 15 | 0.2039265 |
| 20 | 0.271902 |
| 25 | 0.3398775 |
| 30 | 0.407853 |
| 40 | 0.543804 |
| 50 | 0.679755 |
| 60 | 0.815706 |
| 70 | 0.951657 |
| 80 | 1.087608 |
| 90 | 1.223559 |
| 100 | 1.35951 |
| 150 | 2.039265 |
| 200 | 2.71902 |
| 250 | 3.398775 |
| 300 | 4.07853 |
| 400 | 5.43804 |
| 500 | 6.79755 |
| 600 | 8.15706 |
| 700 | 9.51657 |
| 800 | 10.87608 |
| 900 | 12.23559 |
| 1000 | 13.5951 |
| 2000 | 27.1902 |
| 3000 | 40.7853 |
| 4000 | 54.3804 |
| 5000 | 67.9755 |
| 10000 | 135.951 |
| 25000 | 339.8775 |
| 50000 | 679.755 |
| 100000 | 1359.51 |
| 250000 | 3398.775 |
| 500000 | 6797.55 |
| 1000000 | 13595.1 |
What is the centimeter of mercury?
The centimeter of mercury (cmHg) is a unit of pressure equal to the pressure exerted by a one-centimeter-high column of mercury under standard conditions. It is a scaled-up form of the millimeter of mercury (torr) used in some scientific and industrial settings.
Definition
The conventional centimeter of mercury is based on a 1 cm column of mercury with a density of 13,595.1 kg/m³ under standard gravity (9.80665 m/s²):
Exactly, 1 cmHg = 1333.22387415 Pa, which is ten times the millimeter of mercury (1 mmHg ≈ 133.322 Pa). This equals 10 torr under the conventional definition.
Origin and History
The unit descends directly from Torricelli's mercury barometer of 1643, where atmospheric pressure was read as the height of a mercury column. Mercury's high density makes the column compact and easy to read. The conventional value fixes mercury's density (its value at 0 °C) and standard gravity so the unit is independent of temperature and location.
Law and Notable Facts
The centimeter of mercury is not an SI unit; the SI unit of pressure is the pascal. It relates to the standard atmosphere as 1 atm = 76 cmHg exactly (by the historical 760 mmHg definition). The millimeter of mercury (mmHg), essentially identical to the torr, remains standard in medicine for blood pressure.
Real-World Examples and Conversions
- 1 cmHg = 10 mmHg (10 torr) ≈ 1.33322 kPa.
- One standard atmosphere equals exactly 76 cmHg.
- A blood pressure of 120/80 mmHg corresponds to 12/8 cmHg.
- A vacuum of 5 cmHg absolute is about 6.7 kPa, roughly 93% below atmospheric pressure.
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 centimeter of mercury?
One centimeter of mercury equals 0.0135951 technical atmospheres, where one technical atmosphere is one kilogram-force per square centimeter.
How does the technical atmosphere differ from the standard atmosphere?
The technical atmosphere (at) is defined as 1 kgf/cm² ≈ 98066.5 Pa, slightly less than the standard atmosphere's 101325 Pa, so the two are not interchangeable.
How do I convert technical atmospheres back to centimeters of mercury?
Multiply the technical-atmosphere value by 73.55591, the reciprocal of 0.0135951.
Where is the technical atmosphere still used?
It appears in older European engineering for boilers, hydraulic systems, and pressure vessels rated in kgf/cm².
What is 100 cmHg in technical atmospheres?
100 cmHg equals about 1.35951 at (100 × 0.0135951).
People also convert
Complete centimeters of mercury conversion table
| Unit | Result |
|---|---|
| pascals (Pa) | 1333.224 Pa |
| kilopascals (kPa) | 1.333224 kPa |
| megapascals (MPa) | 0.001333224 MPa |
| hectopascals (hPa) | 13.33224 hPa |
| millibar (mbar) | 13.33224 mbar |
| bar (bar) | 0.01333224 bar |
| torr (torr) | 10 torr |
| meters of water @ 4°C (mH2O) | 0.135951 mH2O |
| millimeters of mercury (mmHg) | 10 mmHg |
| standard atmospheres (atm) | 0.0131579 atm |
| centimeters of water (cmH2O) | 13.5951 cmH2O |
| technical atmospheres (at) | 0.0135951 at |
| pounds per square inch (psi) | 0.1933678 psi |
| kilopound per square inch (ksi) | 0.0001933678 ksi |
| Inches of mercury (inHg) | 0.3937008 inHg |