What is the ratio of specific heat of air ?

the specific heat ratio (Cv/Cp) for air at standard conditons is1.4.

Specific Heat Capacities of AirThe nominal values used for air at300 K are CP=1.00 kJ/kg.K, Cv=0.718 kJ/kg.K,, and k =1.4. However they are all functions of temperature, and with the extremely high temperature range experienced in internal combustion and gas turbine engines one can obtain significant errors. The table following gives the values of specific heat capacities as a function of temperature. We find that choosing values of specific heat capacities at the average temperature of each process gives results with reasonable accuracy (within around1%).Ideal gas specific heat capacities of air Temp - CP - Cv - sp.heat250k1.0030.7161.401300k1.0050.7181.400350k1.0080.7211.398 The values up to1000 K were originally published in "Tables of Thermal Properties of Gases", NBS Circular564,1955. The last five rows were calculated from a formula by B G Kyle "Chemical and Process Thermodynamics", Englewood Cliffs / Prentice Hall,1984, and have <1% error.