Pressure is a fundamental physical quantity defined as force applied perpendicular to the surface of an object per unit area. In engineering, two of the most common units used to quantify this are the Pound per square inch (psi) and the Bar (bar).
Pound per square inch (psi): Primarily used in the United States and the oil and gas industry, psi represents the pressure resulting from a force of one pound-force applied to an area of one square inch.
Bar (bar): A metric unit of pressure, though not an SI unit, it is widely accepted for use with SI. One bar is defined as exactly \(10^5\) pascals. It is the standard unit for pressure in many industrial and meteorological applications globally.
The conversion factor between these two units is derived from the definition of the pound and the inch in metric terms. To convert psi to bar, we use the relationship: \(1 \text{ psi} \approx 0.06894757 \text{ bar}\).
Pound per square inch to Bar Conversion Reference Table
Pound per square inch (psi)
Bar (bar)
0.1
0.0069
0.5
0.0345
1.0
0.0689
2.0
0.1379
5.0
0.3447
10.0
0.6895
20.0
1.379
50.0
3.4474
100.0
6.8948
500.0
34.4738
1000.0
68.9476
Conversion Example: 10 psi to Bar
To convert a pressure value from psi to bar, multiply the given psi value by the conversion factor of 0.06894757.
The bar is preferred because it is a metric unit that is very close to standard atmospheric pressure (1 atm = 1.01325 bar), making it intuitive for scientific and industrial calculations compared to the imperial psi.
For most general engineering applications, rounding to four decimal places (0.0689 bar) is sufficient. However, for high-precision calibration or aerospace applications, use the full factor of 0.06894757.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)