|Unit system||SI unit|
|Unit of||Pressure or stress|
|Named after||Blaise Pascal|
|1 Pa in ...||... is equal to ...|
|SI base units:||kg⋅m−1⋅s−2|
|US customary units:||1.450×10−4 psi|
The pascal (symbol: Pa) is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as one newton per square metre. The unit of measurement called standard atmosphere (atm) is defined as 101325 Pa.
Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa) which is equal to one millibar, and the kilopascal (1 kPa = 1000 Pa) which is equal to one centibar. Meteorological forecasts typically report atmospheric pressure in hectopascals per the recommendation of the World Meteorological Organization. Forecasts in the United States typically use millibars, in Canada these reports are given in kilopascals.
The unit is named after Blaise Pascal, noted for his contributions to hydrodynamics and hydrostatics, and experiments with a barometer. The name pascal was adopted for the SI unit newton per square metre (N/m2) by the 14th General Conference on Weights and Measures in 1971.
One pascal is the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square metre.
The unit of measurement called an atmosphere or a standard atmosphere (atm) is 101325 Pa (101.325 kPa). This value is often used as a reference pressure and specified as such in some national and international standards, such as the International Organization for Standardization's ISO 2787 (pneumatic tools and compressors), ISO 2533 (aerospace) and ISO 5024 (petroleum). In contrast, International Union of Pure and Applied Chemistry (IUPAC) recommends the use of 100 kPa as a standard pressure when reporting the properties of substances.
Unicode has dedicated code-points U+33A9 ㎩ SQUARE PA and U+33AA ㎪ SQUARE KPA in the CJK Compatibility block, but these exist only for backward-compatibility with some older ideographic character-sets and are therefore deprecated.
This section needs additional citations for verification. (January 2016) (Learn how and when to remove this template message)
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.
In materials science and engineering, the pascal measures the stiffness, tensile strength and compressive strength of materials. In engineering use, because the pascal represents a very small quantity, the megapascal (MPa) is the preferred unit for these uses.
|nylon 6||2–4 GPa|
|hemp fibre||35 GPa|
|tooth enamel||83 GPa|
|structural steel||200 GPa|
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.
In measurements of sound pressure or loudness of sound, one pascal is equal to 94 decibels sound pressure level (SPL). The quietest sound a human can hear, known as the threshold of hearing, is 0 dB SPL, or 20 µPa.
In medicine, blood pressure is measured in millimeters of mercury (mm Hg). The normal adult blood pressure is < 120 mm Hg Systolic BP (SBP) and < 80 mm Hg Diastolic BP (DBP). Convert mm Hg to SI units as follows: 1 mm Hg = 0.13332 kPa . Hence normal blood pressure in SI units is < 16.0 kPa SBP and < 10.7 kPa.
Hectopascal and millibar units
The units of atmospheric pressure commonly used in meteorology were formerly the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of SI units, meteorologists generally measure pressures in hectopascals (hPa) unit, 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 excludes the hectopascal from use.
Many countries also use millibars. In practically all other fields, the kilopascal (1000 pascals) is used instead.
- Atmospheric pressure which gives the usage of the hbar and the mbar
- Centimetre of water
- Metric prefix
- Orders of magnitude (pressure)
- Pascal's law
- Pressure measurement
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), p. 118, ISBN 92-822-2213-6, archived (PDF) from the original on 14 August 2017
- "Definition of the standard atmosphere". BIPM. Retrieved 16 February 2015.
- "US government atmospheric pressure map".
- "The Weather Channel".
- Canada, Environment (16 April 2013). "Canadian Weather - Environment Canada". weather.gc.ca.
- bipm.fr Archived 30 June 2007 at the Wayback Machine
- Minutes of the 14. General Conference on Weights and Measures, 1971, page 78
- Table 3 (Section 2.2.2) Archived 18 June 2007 at the Wayback Machine, SI Brochure, International Bureau of Weights and Measures
- "Resolution 4 of the 10th meeting of the CGPM". Conférence Générale des Poids et Mesures. 1954. Retrieved 5 April 2010.
- IUPAC.org, Gold Book, Standard Pressure
- "CJK Compatibility" (PDF). 2015. Retrieved 21 February 2016.
- The Unicode Standard, Version 8.0.0. Mountain View, CA: The Unicode Consortium. 2015. ISBN 978-1-936213-10-8. Retrieved 21 February 2016.
- "Tensile Modulus - Modulus of Elasticity or Young's Modulus - for some common Materials". Retrieved 16 February 2015.
- "Chapter 7 ResNet Standards: ResNet National Standard for Home Energy Audits" (PDF). ResNet. 2010. Archived from the original (PDF) on 26 July 2011. Retrieved 3 March 2011.
- "BP Guideline | Target:BP". American Heart Association. American Heart Association. Retrieved 18 May 2020.
- "Convert mm Hg to kPa - Conversion of Measurement Units". www.convertunits.com. Retrieved 18 May 2020.
- "KNMI - Weer - Waarnemingen". Retrieved 4 December 2016.
- "Comment convertir la pression? - IRM". Retrieved 4 December 2016.
- "DWD". Archived from the original on 10 February 2008. Retrieved 20 December 2006.
- "Japan Meteorological Agency - Weather Maps". Retrieved 4 December 2016.
- "MDD". Archived from the original on 6 May 2006.
- United Kingdom, Met Office. "Key to symbols and terms". Retrieved 4 December 2016.
- "CTV News, weather; current conditions in Montreal". Archived from the original on 4 June 2011.
- Canada, Environment. "Montréal, QC - 7 Day Forecast - Environment Canada". Retrieved 4 December 2016.
- Ambler Thompson (Editor) Guide for the Use of the International System of Units (SI) (rev. ): The ..., p. 66, at Google Books