Millimeters Of Water to PSI (mmH₂O to psi)

1 millimeter of water equals 0.001422334331 pounds per square inch (rounded).

1 millimeter of water = 0.001422334331 pounds per square inch

How to convert millimeters of water to pounds per square inch

To convert millimeters of water to pounds per square inch, multiply the number of millimeters of water by 0.001422334331. The factor is rounded to 10 significant digits. To go the other way, multiply pounds per square inch by 703.0695796 (rounded).

pounds per square inch = millimeters of water × 0.001422334331

Example: 10 millimeters of water = 0.01422334331 pounds per square inch.

About these units

Millimeter Of Water (mmH₂O)

ScientificCurrent unit

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

Pound Per Square Inch (psi)

US & ImperialCurrent unit

About 6,894.757 pascals. The common unit for tire pressure, hydraulics and gas pipelines in the US.

Unlike most pressure units, psi has no namesake: it simply spells out its own definition, one pound-force acting on one square inch, and it is based on avoirdupois units. Used mainly in the United States, it is about 6.895 kilopascals.

The letters after the unit matter. Psia is measured against a vacuum, while psig is measured against the surrounding air, so at sea level, where the atmosphere is about 14.7 psi, you add that amount to a gauge reading to get an absolute one. A bicycle tire at 65 psig is therefore at 79.7 psia, and the label psid means a difference between two pressures rather than a reference to ambient air.

Typical automobile tires are listed at about 32 psig, and road racing bicycle tires at about 120 psig. One standard atmosphere is 14.696 psi, which gives a feel for how many multiples of sea-level air those tire pressures represent.

1 pound per square inch = 6,894.757293 pascals (approximately).

Sources: Wikipedia: Pounds per square inch; Wikipedia: Standard atmosphere (unit)

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