A relationship between the dimensionless thermoelectric figure of merit, ZT, and the ratio of the open-circuit temperature difference, ΔTo, and the short-circuit temperature difference, ΔTs, is reported. Equivalent relationship between ZT and the open circuit voltage, Vo, and short-circuit current, Is, are also obtained. Both relationships provide a theoretical basis for the development of a novel, user-friendly and low cost technique for rapid and accurate measurement of the thermoelectric dimensionless figure of merit.