Standard state pressure
| Value | 100,000 Pa |
| Status | Exact by definition — no uncertainty |
| Source | IUPAC (1982); SI Brochure, 9th edition |
| Categories | ThermodynamicChemistry |
Standard state pressure in every pressure unit
| microbar | 1,000,000 μbar |
| barye | 1,000,000 Ba |
| millitorr | 750,061.68 mTorr |
| pascal | 100,000 Pa |
| millimeter of water column | 10,197.162 mmH₂O |
| pound per square foot | 2,088.5434 lb/ft² |
| centimeter of water column | 1,019.7162 cmH₂O |
| hectopascal | 1,000 hPa |
| millibar | 1,000 mbar |
| torr | 750.06168 Torr |
| millimeter of mercury | 750.06158 mmHg |
| inch of water column | 401.46308 in w.g. |
| kilopascal | 100 kPa |
| foot of water column | 33.455257 ft H₂O |
| inch of mercury | 29.529983 inHg |
| pound per square inch | 14.503774 psi |
| meter of water column | 10.197162 m H₂O |
| decibar | 10 dbar |
| kilogram-force per square centimeter | 1.0197162 kgf/cm² |
| bar | 1 bar |
| atmosphere | 0.98692327 atm |
| megapascal | 0.1 MPa |
| kip per square inch | 0.014503774 ksi |
| gigapascal | 0.0001 GPa |
| million pounds per square inch | 0.000014503774 Mpsi |
Learning zone
Every standard enthalpy of formation, standard entropy and equilibrium constant is quoted relative to a reference pressure, and since 1982 IUPAC's is exactly 1 bar = 100 000 Pa. The superscript degree symbol in ΔG° means "at p° = 1 bar", and the partial pressures inside an equilibrium constant are divided by it — which is why K is dimensionless.
Older tables use 1 atm = 101.325 kPa, a 1.3 % difference. For most reactions it shifts ΔG° by only tens of joules per mole, but it changes tabulated standard entropies of gases by R ln(1.01325) ≈ 0.109 J/(mol·K), enough to matter in precise work. Standard state fixes pressure only; the temperature is whatever the table says, conventionally 298.15 K.