Convert Millimeter of Water to Attopascal (mmH2O to Attopascal)

Millimeter of Water (mmH2O) and Attopascal (Attopascal) are both units of pressure. With the conversion form below, you can effortlessly and accurately convert millimeter of water to attopascal. This free online calculator tool makes it simple and easy to perform the conversion from mmH2O unit to the Attopascal unit.

Pressure is the force applied perpendicular to a surface per unit area: P = F / A. The SI unit is the pascal (Pa), equal to one newton per square metre (1 Pa = 1 N/m²). Practical applications use larger units: the bar (1 bar = 100,000 Pa, close to standard atmospheric pressure), atmosphere (atm) (1 atm = 101,325 Pa), and psi (pounds per square inch, used in the US for tire and gas pressures). Blood pressure is measured in mmHg (millimetres of mercury), also called torr.

The millimeter of water (symbol: mmH₂O or mmH2O) is a non-SI unit of pressure defined as the pressure exerted by a one-millimeter column of water under standard gravity. It is commonly used in ventilation systems, clean rooms, HVAC engineering, and laboratory instruments to measure small pressure differences. Although the pascal is the SI unit of pressure, the millimeter of water remains a practical unit for low-pressure applications. It is based on the concept of a water column.

One millimeter of water is equal to 9.80665 pascals, 0.1 centimeter of water, 0.0000980665 bar, 0.00142233 pounds per square inch, and 0.00980665 kilopascal. The millimeter of water is widely used for measuring very low gas and liquid pressures.

The attopascal (symbol: aPa) is an SI-derived unit of pressure equal to one quintillionth (10^-18) of a pascal. It is an extremely small pressure unit used mainly in theoretical physics, nanotechnology, and scientific research involving ultra-low pressure measurements. The attopascal uses the SI prefix atto, representing a factor of 10^-18.

One attopascal is equal to 0.000000000000000001 pascal, 0.001 femtopascal, 0.000000001 nanopascal, 1×10^-23 bar, and 9.86923×10^-24 standard atmosphere. Although rarely used outside research, the attopascal is part of the complete SI pressure scale.