Enthalpy from dry bulb temperature and humidity
Enter the dry bulb temperature in °F, the relative humidity and the barometric pressure in inHg or psia (29.92 inHg is sea level). The page works through the saturation vapor pressure and the partial vapor pressure to the humidity ratio and the specific enthalpy, and also reports the humidity ratio at saturation for the same state together with the saturation ratio. Enthalpy in Btu/lb uses h = 0.240t + W(1061 + 0.444t) with t in °F, the SI figure in kJ/kg uses h = 1.006t + W(2501 + 1.86t) with t in °C, and the humidity ratio uses W = 0.622pv / (p - pv).
Both equations and the saturation vapor pressure equation come from secondary air conditioning material. Some sources publish the enthalpy coefficients as 1.005, 2500.9 and 1.805, so the set used here is printed with the results. The two enthalpy figures do not convert directly, because the US convention sets h to zero for dry air at 0 °F while the SI convention sets it to zero at 0 °C. Figures are current as of October 2026.
Dew point is not covered, and neither is wet bulb input or chart plotting. Specific volume is left out because the constant it needs has not been confirmed in an authoritative source. This calculator is for reference and does not replace design work; review by a qualified engineer is required.
Frequently Asked Questions
No. This page takes only dry bulb temperature, relative humidity and barometric pressure as inputs.
Dew point is handled by a separate tool. This page stays on enthalpy and humidity ratio so the two sets of results do not overlap.
It is the current humidity ratio divided by the humidity ratio at saturation for the same temperature and pressure. It lands near the relative humidity but is defined differently.