Download the information in Excel format: Hydrogen Properties

Properties Description Values Units

Autoignition temperature

The autoignition temperature depends on hydrogen concentration (minimum at stoichiometric combustion conditions), pressure, and even the surface characteristics of the vessel. See NFPA 2: Hydrogen Technologies Code 2016 Edition Annex D. 500 °C
    932 °F
Boiling point (1 atm) NIST Chemistry WebBook -252.9 °C
    -423.2 °F
Density (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 0.08375 kg/m³
    0.005229 lb/ft³
Diffusion coefficient in air (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. National Aeronautical and Space Administration, Safety Standard for Hydrogen and Hydrogen Systems (NSS 1740.16), 1997 0.610 cm²/s
    6.57 E-4 ft²/s
Enthalpy (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 3858.1 kJ/kg
    1659.8 Btu/lb
Entropy NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 53.14 J/g-K
    12.70 Btu/lb-°R
Flame temperature in air National Aeronautical and Space Administration, Safety Standard for Hydrogen and Hydrogen Systems (NSS 1740.16), 1997 2045 °C
    3713 °F
Flammable range in air NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. National Aeronautical and Space Administration, Safety Standard for Hydrogen and Hydrogen Systems (NSS 1740.16), 1997 4.0 - 75.0 vol%
Ignition energy in air Hydrogen Fuel Cell Engines and Related Technologies. Module 1: Hydrogen Properties. U.S. DOE. 2001 2.0 E-5 J
    1.9 E-8 Btu
Internal Energy (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. Reference state: Internal Energy U=0 at 273.16 K for saturated liquid; Entropy S=0 at 273.16 K for saturated liquid. NIST Chemistry WebBook 2648.3 kJ/kg
    1139.3 Btu/lb
Molecular weight NIST Chemistry WebBook 2.02  
Specific gravity (air = 1) (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. Hydrogen Fuel Cell Engines and Related Technologies. Module 1: Hydrogen Properties. U.S. DOE. 2001 0.0696  
Specific volume (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 11.94 m³/kg
    191.26 ft³/lb
Specific heat at constant pressure, Cp (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 14.29 J/g-K
    3.415 Btu/lb-°R
Specific heat at constant volume, Cv (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 10.16 J/g-K
    2.428 Btu/lb-°R
Thermal conductivity (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 0.1825 W/m-K
    0.1054 Btu/ft-h-°R
Viscosity (NTP) NTP (normal temperature and pressure) = 20°C (68°F) and 1 atm. NIST Chemistry WebBook 8.813 E-5 g/cm-sec
    5.922 E-6 lb/ft-sec