Molar volume of an ideal gas at 25 °C and 1 atm

V_{\mathrm{m}}^{\,\mathrm{NTP}} = 24.4654037\ \text{L/mol}

Value	24.4654037 L/mol
Status	Exact by definition — no uncertainty
Source	Derived from CODATA 2022 R at 298.15 K, 101325 Pa
Categories	Thermodynamic Chemistry

Learning zone

Room-temperature work rarely happens at 0 °C, so industrial hygiene, air quality and HVAC calculations use 25 °C and 1 atm — often labelled NTP, sometimes SATP. One mole then fills 24.4654 L. This is the number hiding inside the standard conversion between ppm by volume and mg/m³ for a gaseous contaminant: mg/m³ = ppm × M / 24.4654.

Be warned that the labels are not standardised. NIST's NTP is 20 °C and 1 atm, giving 24.0555 L/mol; IUPAC's SATP is 25 °C and 1 bar, giving 24.7896 L/mol; and the reference conditions written into gas-sales contracts are different again, often 60 °F and 14.696 psia. Always carry the temperature and pressure with the number rather than the acronym.

Used by these solvers

Ideal Gas Law

P V = n R T

Gas Volume at STP

V = n\,V_m

Partial Pressure from Mole Fraction

P_i = x_i \, P_{\text{total}}