Consider we have an inertial frame of reference  and a rotating frame of reference  which both are sharing common origin . Assume that frame  is rotating around a fixed axis with angular velocity . Now assuming fluid velocity to be  and fluid velocity relative to rotating frame of reference to be :
Rothalpy of a fluid point  can be defined as
where  and  and  is the stagnation enthalpy of fluid point  relative to the rotating frame of reference , which is given by
and is known as relative stagnation enthalpy.
Rothalpy can also be defined in terms of absolute stagnation enthalpy:
where  is tangential component of fluid velocity .