Millimeters Of Water to Standard Atmospheres (mmH₂O to atm)
1 millimeter of water equals 0.00009678411054 standard atmospheres (rounded).
How to convert millimeters of water to standard atmospheres
To convert millimeters of water to standard atmospheres, multiply the number of millimeters of water by 0.00009678411054. The factor is rounded to 10 significant digits. To go the other way, multiply standard atmospheres by 10,332.27453 (rounded).
standard atmospheres = millimeters of water × 0.00009678411054
Example: 10 millimeters of water = 0.0009678411054 standard atmospheres.
About these units
Millimeter Of Water (mmH₂O)
Exactly 9.80665 pascals by convention. Used for very low pressures.
A column of water one millimetre tall presses down with 9.80665 Pa under the usual convention, which assumes a density of 1,000 kg/m3 for water at its densest, near 4 degrees Celsius, and standard gravity. NIST marks this conventional millimeter of water as an exact factor. Using the true density of water at 4 degrees Celsius, 999.972 kg/m3, gives about 9.80638 Pa instead, so the two differ in the fifth digit.
Because the unit is so small it suits very low pressures, such as the draft in a duct or a chimney, filter drops and sensitive gauges. It also gives waterproof ratings for fabric, where a tent or jacket rated to some number of millimetres can resist that height of water before leaking. Pressure in this form is often written mmH2O, mmWG or mmWC. Ten millimetres of water is about 98 Pa, or roughly 0.1 percent of one standard atmosphere.
1 millimeter of water = 9.80665 pascals (exactly).
Sources: Wikipedia: Millimetre of water; NIST SP 811, Appendix B.8
Standard Atmosphere (atm)
Exactly 101,325 pascals, the average pressure of the atmosphere at sea level.
A column of mercury about 76 cm tall was Torricelli's measure of the air, and the standard atmosphere began as exactly that: the pressure of 760 mm of mercury at 0 degrees Celsius under standard gravity. It was used as a reference for physical and chemical properties, and the Celsius scale set 100 degrees as the boiling point of water at that pressure.
In 1954 the 10th CGPM confirmed the standard atmosphere as exactly 1,013,250 dynes per square centimeter, which is 101,325 pascals, a definition that no longer depends on the properties of any substance.
In practice one atmosphere is about 1.01325 bar, 760 mmHg, 14.696 psi or 29.92 inHg, and roughly the pressure of 10.33 meters of water. Chemistry splits on it: until 1982 standard temperature and pressure used 1 atm, but that year IUPAC recommended a standard pressure of exactly 100 kPa instead.
1 standard atmosphere = 101,325 pascals (exactly).
Sources: Wikipedia: Standard atmosphere (unit); Wikipedia: Atmospheric pressure; Wikipedia: Evangelista Torricelli
Related conversions
- Standard atmospheres to millimeters of water (reverse)
- Millimeters of water to pascals
- Millimeters of water to kilopascals
- Millimeters of water to bars
- Millimeters of water to PSI
- Pascals to standard atmospheres
- Kilopascals to standard atmospheres
- Bars to standard atmospheres
- PSI to standard atmospheres
- Hectopascals to standard atmospheres
- Megapascals to standard atmospheres
- Millibars to standard atmospheres
- Torr to standard atmospheres
- Millimeters of mercury to standard atmospheres
- Inches of mercury to standard atmospheres
- Gigapascals to standard atmospheres
- Kilopounds per square inch to standard atmospheres
See all pressure units.