Helium - Thermophysical Properties

Chemical, physical and thermal properties of Helium (He) at 25°C (77°F, 298 K) and atmospheric pressure. Includes molecular weight, density, viscosity, specific heat, thermal conductivity, and other thermodynamic properties in both imperial and metric units.

PropertyValueUnit
Molecular Weight4.0026g/mol
Specific Gravity (air = 1)0.138-
Specific Volume97.86 / 6.11ft³/lb / m³/kg
Density of liquid at atmospheric pressure7.80 / 125lb/ft³ / kg/m³
Absolute Viscosity13.4×10⁻⁶ / 0.02lbm/ft·s / cP
Sound velocity in gas1015m/s
Specific Heat (cp)1.24 / 5188Btu/lb·°F / J/kg·K
Specific Heat Ratio (cp/cv)1.66-
Gas constant (R)386 / 2077ft·lb/lb·°R / J/kg·°C
Thermal Conductivity0.086 / 0.149Btu/hr·ft·°F / W/m·°C
Boiling Point-452 / 4.22°F / K
Latent Heat of Evaporation10.0 / 23300Btu/lb / J/kg
Critical Temperature-450.3 / 5.2°F / K
Critical Pressure33.22psia
Critical Volume0.231 / 0.0144ft³/lb / m³/kg
FlammableNo-

Reference Information

Standard Conditions: 25°C (77°F, 298 K) and atmospheric pressure

Property Units:

  • Imperial: ft³/lb, Btu/lb·°F, lbm/ft·s, Btu/hr·ft·°F
  • Metric: m³/kg, J/kg·K, cP (centipoise), W/m·°C

Related Resources:

  • Density and specific weight at varying pressure and temperature
  • Atmospheric pressure reference
  • STP - Standard Temperature and Pressure
  • Comparable thermophysical properties for other gases and liquids

Safety: Helium is non-flammable and inert.