Theory of thermoelectricity defines the emf of a thermocouple through the difference in the absolute thermoelectric power (S) between two metals or alloys that constitute the thermocouple. No general relationship for the S(T) was found so far, because the functions differ for different thermoelectric materials, increasing and/or decreasing with temperature, changing sign, slope, etc. We show that the emf of a thermocouple is in fact a universal function of temperature, increasing similar to T-2 at low temperatures and similar to T at high temperatures. (C) 2009 Elsevier B.V. All rights reserved.