A portable thermocouple probe is designed with physical and geometric properties such that its principal performance characteristics can be predicted from relatively uncomplicated mathematical models. Theory and experiment show that usual thermocouple errors and surface‐temperature perturbations can be kept unimportant in a variety of practical applications. Techniques are described for using the probe to measure temperature of stationary and moving materials, including thermal insulating materials and thin sheets where temperature is normally severely perturbed during contact measurements. It is convenient to use the device in combination with a battery‐operated digital readout device, permitting temperatures within a few hundred degrees of ambient to be measured with an accuracy of ±2° and a response speed of about 2 s. The probe is found well suited for use in the heat‐transfer laboratory, in the factory, and in energy‐conservaton field work.