In any grinding operation heat flows periodically into the abrasive grains in the surface of the wheel during wheel-work contact and is extracted during the remaining portion of a single revolution of the wheel. If it can be assumed that all of the heat flowing inward is extracted outward during the cooling portion of a single wheel revolution, then the thermal partition coefficient R=heattowork/totalgrindingenergy may be readily estimated. This paper discusses conditions under which this assumption represents an acceptable approximation.