Is a bar the same as an atmosphere? No: the bar is exactly 100,000 pascals, the standard atmosphere exactly 101,325 and the technical atmosphere exactly 98,066.5. This pressure converter lists 52 units, from the attopascal to the exapascal, and keeps those three apart.
THREE ATMOSPHERES, SIX UNITS
| Reference | Pa | bar | atm | at | psi | torr |
|---|---|---|---|---|---|---|
| 1 bar | 100,000 | 1 | 0.9869233 | 1.019716 | 14.50377 | 750.0617 |
| 1 standard atmosphere | 101,325 | 1.01325 | 1 | 1.033227 | 14.69595 | 760 |
| 1 technical atmosphere | 98,066.5 | 0.980665 | 0.9678411 | 1 | 14.22334 | 735.5592 |
By direct calculation with 50-digit arithmetic. The symbol atm is the standard atmosphere and at the technical atmosphere.
Pressure Converter
Complete list of pressure units
| Unit | 1 unit in pascals |
|---|
Shaded rows use the exact values of the panel on tables that are off. A red mark on the left shows units that share one value.
Definition: the Pascal, the Bar, the Psi and 52 Units
The pascal is the SI derived unit of pressure: the pressure exerted by a force of 1 newton applied perpendicularly to an area of one square meter, written 1 N/m² or 1 kg/m·s². A kilopascal is 1,000 pascals. A bar is defined as exactly 100,000 pascals, which is about 0.987 standard atmospheres, the unit often used as a reference of standard pressure and equal to exactly 101,325 pascals.
A pound-force per square inch, the psi, is the pressure that results when a force of one pound-force is applied to an area of one square inch. It is approximately 6,895 pascals and exactly 6,894.757293168 pascals: a copy of Wikipedia's article on the pound-force gives the pound-force as exactly 0.45359237 kg × 9.80665 m/s², which is 4.4482216152605 newtons, and Wikipedia's table for the kilogram-force per square centimeter gives 6,894.757293168 pascals for the psi, with the inch at exactly 0.0254 m.
Around those anchors the converter lists the SI-prefixed pascals from the exapascal to the attopascal, units built on the newton per area, the millibar and the microbar, the dyne per square centimeter, units based on the kilogram-force and the gram-force, the short and long ton-force, the kip-force, the pound-force per square inch and per square foot, the poundal per square foot, the torr, columns of mercury and of water at stated temperatures, and the technical atmosphere. Eight groups of units share one value, such as pascal and newton per square meter, hectopascal and millibar, or the technical atmosphere and the kilogram-force per square centimeter, which makes 43 distinct values behind 52 names.
History and Origin
The pascal is named after Blaise Pascal, a French mathematician and physicist, and the kilopascal is simply a multiple of it, as is common within the SI. In 1971, at the 14th General Conference on Weights and Measures, the pascal was adopted as the SI derived unit of pressure. The bar was introduced by Vilhelm Bjerknes, a Norwegian meteorologist who founded modern weather forecasting, and its name comes from the Greek word “baros”, which means weight.
The psi originated in the imperial and US customary systems and is based on the avoirdupois system, which uses weights in terms of the avoirdupois pound, standardized in 1959. That system is believed to have come into use in England around 1300 and was used in the international wool trade, so the prototype pound of the time was known as the avoirdupois wool pound.
Current Use, and Columns of Liquid
The kilopascal is widely used in countries that have adopted the SI, and mostly in scientific contexts such as materials science, engineering and geophysics, including in the United States, where the psi is more common in everyday life. The psi measures tire pressure, scuba tank pressure and natural gas pipeline pressure, among others. The bar is a metric unit but is not accepted within the SI and is deprecated in certain fields, although authors remain free to use it. Millibars are common for atmospheric pressure, where standard pressure is 1013.25 mbar, or 101.325 kPa, and meteorologists use them because pascals would give much larger values.
A bar to psi conversion multiplies by 14.503773773, so 15 bar is 217.556606595 psi, and a psi to bar conversion multiplies by 0.0689475729. A kpa to psi conversion multiplies by 0.1450377377, so 15 kPa is 2.175566066 psi, and a psi to kpa conversion multiplies by 6.8947572932.
Some units depend on temperature. An inch of mercury at 32 °F is 0.28% larger than at 60 °F, and an inch of water at 4 °C is 0.10% larger than at 60 °F. The torr is exactly 101,325/760 pascals, which is 133.3223684211. The technical atmosphere is one kilogram-force per square centimeter, which is exactly 98,066.5 pascals according to an online units handbook.
Frequently Asked Questions
How many psi are in a bar?
14.503773773, so 15 bar is 217.556606595 psi.
How many pascals are in a psi?
Exactly 6,894.757293168, which is approximately 6,895.
Is a bar the same as an atmosphere?
No. A bar is 0.9869233 standard atmosphere, and a standard atmosphere is 1.01325 bar.
How many pascals are in a standard atmosphere?
Exactly 101,325, which is 760 torr.
How many bar are in a technical atmosphere?
0.980665, since a technical atmosphere is 98,066.5 pascals.
Method and sources. Every factor was checked against its exact definition with 50-digit arithmetic. The exact values of the psi and of the technical atmosphere rest on a copy of an encyclopedia article, on an encyclopedia table and on an online units handbook, not on a primary standards page.
This converter is provided for general reference. For engineering, medical, diving or aviation work, use the unit and the standard the document specifies. Written by Staff Editorial, NumeraHub.