At STP (0 °C, 1 atm): 1 mol gas = 22.414 L
STP is defined as 0 °C (273.15 K) and 1 atm (101.325 kPa). At STP, one mole of an ideal gas occupies exactly 22.414 L (the molar volume). IUPAC updated STP to 0°C and 1 bar (100 kPa) in 1982, giving a molar volume of 22.711 L, but the traditional 1 atm definition is still widely used in education. Gas density at STP = molar mass / 22.414 (in g/L). Common gas densities at STP: H₂ = 0.090, He = 0.179, N₂ = 1.251, O₂ = 1.429, Ar = 1.784, CO₂ = 1.977 g/L. STP is the reference point for gas calculations, flow rate specifications, and comparing properties of different gases. To convert to other conditions, use PV/T = P₀V₀/T₀.