## standard pressure

https://doi.org/10.1351/goldbook.S05921
Chosen value of pressure denoted by $$p^{\unicode{x29B5}}$$ or $$p^{\,\unicode{x26ac}}$$. In 1982 IUPAC recommended the value $$10^{5}\ \text{Pa}$$, but prior to 1982 the value $$101\ 325\ \text{Pa}$$ (= $$1\ \text{atm}$$) was usually used.
Sources:
Green Book, 2nd ed., p. 54 [Terms] [Book]
PAC, 1994, 66, 533. (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994)) on page 536 [Terms] [Paper]