ELMHURST COLLEGE
PHYSICS 313 Thermodynamics
| Conversion Factors Between Common Units of Pressure
Each number gives the value of 1 unit of the pressure named at the left in terms of the unit named at the top; | ||||||
UNITS |
pascal
(N/m2 or Pa) |
lb/in.2 |
atm |
bar |
mmHg
or Torr |
cmH20 |
| pascal (N/m2 or Pa) = | 1 | 1.45 x 10-4 | 9.87 x 10-6 | 10-5 | 7.50 x 10-3 | 1.02 x 10-2 |
| lb/in.2 = | 6.89 x 103 | 1 | 6.80 x 10-2 | 6.89 x 10-2 | 51.7 | 70.3 |
| atm = | 1.01 x 105 | 14.7 | 1 | 1.01 | 760 | 1.03 x 103 |
| bar = | 105 | 14.5 | 0.987 | 1 | 750 | 1.07 x 103 |
| mmHg or Torr = | 133 | 1.93 x 10-2 | 1.32 x 10-3 | 1.33 x 10-3 | 1 | 1.36 |
| cmH20 = | 98.1 | 1.42 x 10-2 | 9.68 x 10-4 | 9.81 x 10-4 | 0.736 | 1 |
The dimensions of pressure are [p] = [Force/length2] = [F/2 ].
Definition
The SI unit of pressure is the pascal (Pa), which is one Newton per square meter (N/m2): 1 Pa = 1 N/m2 .
Unfortunately, this unit is not yet commonly used in practice. More common units are atmospheres (atm), pounds per square inch (lb/in2), millimeters of mercury (mmHg or Torr), and bars. For instance, barometric pressure might be quoted at 989 mbar, whereas blood pressure is quoted as 120 mmHg (or 120 Torr). There are a number of other units that are frequently used in medicine and science, so you must be able to convert readily from one to another. This table gives the conversion factors between the most common units.
Remark: You cannot cancel part of an abbreviation.
In the table, bar, atm, mmHg and cmH20 are abbreviations for the names of units. In a calculation, the mm in mmHg cannot
be canceled the way the m2 in N/m2 can. The four letters mmHg are part of the abbreviation, just like the letters a-t-m.