For general scientific use, *thermal conductance* is the quantity of heat that passes in unit time through a plate of *particular area and thickness* when its opposite faces differ in temperature by one kelvin. For a plate of thermal conductivity *k*, area *A* and thickness *L*, the conductance calculated is *kA*/*L*, measured in W⋅K^{−1} (equivalent to: W/°C). ASTM C168-15, however, defines thermal conductance as "time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces" and defines the units as W/(m^{2}⋅K) (Btu/(h⋅ft^{2}⋅°F))^{[2]}

The thermal conductance of that particular construction is the inverse of the thermal resistance. Thermal conductivity and conductance are analogous to electrical conductivity (A⋅m^{−1}⋅V^{−1}) and electrical conductance (A⋅V^{−1}).

There is also a measure known as heat transfer coefficient: the quantity of heat that passes in unit time through a *unit area* of a plate of particular thickness when its opposite faces differ in temperature by one kelvin. The reciprocal is *thermal insulance*. In summary:

thermal conductance =

*kA*/*L*, measured in W⋅K^{−1}or in ASTM C168-15 as W/(m^{2}⋅K)^{[2]}thermal resistance =

*L*/(*kA*), measured in K⋅W^{−1}(equivalent to: °C/W)heat transfer coefficient =

*k*/*L*, measured in W⋅K^{−1}⋅m^{−2}thermal insulance =

*L*/*k*, measured in K⋅m^{2}⋅W^{−1}.

The heat transfer coefficient is also known as *thermal admittance* in the sense that the material may be seen as admitting heat to flow.