The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the
pounds per square inch (psi) unit, except in some countries that still use the
imperial measurement system or the
US customary system, including the United States.
Geophysicists use the gigapascal (GPa) in measuring or calculating
tectonic stresses and pressures within the
Earth. Medical
elastography measures tissue stiffness non-invasively with
ultrasound or
magnetic resonance imaging, and often displays the
Young's modulus or
shear modulus of tissue in kilopascals. In
materials science and
engineering, the pascal measures the
stiffness,
tensile strength and
compressive strength of materials. In engineering the megapascal (MPa) is the preferred unit for these uses, because the pascal represents a very small quantity. The pascal is also equivalent to the SI unit of
energy density, the joule per cubic metre. This applies not only to the thermodynamics of pressurised gases, but also to the energy density of
electric,
magnetic, and
gravitational fields. The pascal is used to measure
sound pressure.
Loudness is the subjective experience of sound pressure and is measured as a
sound pressure level (SPL) on a logarithmic scale of the sound pressure relative to some reference pressure. For sound in air, a pressure of 20 μPa is considered to be at the
threshold of hearing for humans and is a common reference pressure, so that its SPL is zero.
The airtightness of buildings is measured at 50 Pa. In medicine,
blood pressure is measured in
millimeters of mercury (mmHg, very close to one
Torr). The normal adult blood pressure is less than 120 mmHg systolic BP (SBP) and less than 80 mmHg diastolic BP (DBP). Convert mmHg to SI units as follows: . Hence the normal blood pressure in SI units is less than 16.0 kPa SBP and less than 10.7 kPa DBP. These values are similar to the pressure of water column of average human height; so pressure has to be measured on arm roughly at the level of the heart.
Hectopascal and millibar units The units of
atmospheric pressure commonly used in
meteorology were formerly the
bar (), which is close to the average air pressure on Earth, and the millibar. Since the introduction of
SI units, meteorologists generally measure atmospheric pressure in hectopascals (hPa), equal to 100 pascals or 1 millibar. Exceptions include Canada, which uses kilopascals (kPa). In many other fields of science, prefixes that are a power of 1000 are preferred, which theoretically excludes hectopascal from use. Many countries still use millibars to measure atmospheric pressure. In practically all other fields, the kilopascal is used instead. == Multiples and submultiples ==